(english)
If you have to install XP SP3 you can also download the ISO file to burn a XP SP3 install CD:
Windows XP Service Pack 3 - ISO-9660 CD Image File
Brief Description
Windows® XP Service Pack 3 (SP3) includes all previously released updates for the operating system. This update also includes a small number of new functionalities, which do not significantly change customers’ experience with the operating system.
DO NOT DOWNLOAD IF YOU ARE UPDATING JUST ONE COMPUTER: A smaller, more appropriate download for individual users is now available on Windows Update.

This CD is available in different languages: use the Change Language: on that page there is also a link to Windows Update

(Dutch)
Windows XP Service Pack 3 (32-bit x86) - ISO 9660-cd-kopiebestand
Snelle beschrijving
Windows® XP Service Pack 3 (SP3) bevat alle eerder uitgebrachte updates voor het besturingssysteem. Deze update bevat ook een klein aantal nieuwe functies die de gebruikerservaring van het besturingssysteem niet wezenlijk veranderen.
Niet Downloaden als u slechts één computer wilt updaten. Een kleinere, geschiktere download voor afzonderlijke gebruikers is nu beschikbaar via Windows Update.

De CD is beschikbaar in meerdere talen, gebruik de: Taal wijzigen: feature. Er is ook een link naar Windows Update.

you should not reformat your harddisc:
you could try this:
restart your computer with XP pro cd still in the drive:

Starting the Windows Recovery Console
To start the Windows Recovery Console, use one of the following methods: • Use the Windows Setup floppy disks or the Windows CD-ROM to start your computer. At the "Welcome to Setup" screen, press F10 or press 'R" to repair.
from the prompt enter just:
FIXBOOT [Enter]
FIXMBR [Enter]
BOOTCFG /scan [Enter] Scans all disks for Windows installations and displays the results so that you can specify which installations to add.
BOOTCFG /rebuild [Enter] Iterates through all Windows installations so that you can specify which installations to add.
The rebuild process will step you through a number of steps depending upon how many operating systems you have on the computer and how the computer is setup. Below is a listing of the common steps you are likely going to encounter.

* Prompt for the identified versions of Windows installed. When you receive this prompt press Y if the bootcfg command properly identified each of the Windows operating systems installed on the computer. It is important to realize this command will only detect Windows XP, Windows 2000, and Windows NT installations.

* Prompt to enter the load identifier. This is the name of the operating system for the boot.ini. For example, Microsoft Windows XP Home users would enter "Microsoft Windows XP Home edition".

* Prompt to Enter OS load options. When this prompt is received type /fastdetect to automatically detect the available options.

Once you have completed all the available options in the rebuild and are back at the prompt type exit to reboot the computer.
Description of the Windows XP Recovery Console
How-to repair Windows XP, How to Perform an In-Place Upgrade

Quote:
In previous versions of Windows, correcting an operating system error, or installing a new motherboard, usually meant formating and reinstalling, resulting in loss of all data. Don't worry; Windows XP repair feature won't delete your data, installed programs, personal information, or settings. It just repairs the operating system!

(Dutch)
Windows XP herstellen naar een “net-geinstalleerde” versie, met behoud van data.

I went to Windows Update yesterday and installed the Swedish release of SP3. No problems so far, except the driver and utility program for my D-Link wireless router and usb stick no longer load at startup (they exit with errors). But Windows seems perfectly capable of driving them by itself and everything operates as normal.

Quoting Giga Wizard:

Quote:
you should not reformat your harddisc:
you could try this:
restart your computer with XP pro cd still in the drive:

Starting the Windows Recovery Console
To start the Windows Recovery Console, use one of the following methods: • Use the Windows Setup floppy disks or the Windows CD-ROM to start your computer. At the "Welcome to Setup" screen, press F10 or press 'R" to repair.
from the prompt enter just:
FIXBOOT [Enter]
FIXMBR [Enter]
BOOTCFG /scan [Enter] Scans all disks for Windows installations and displays the results so that you can specify which installations to add.
BOOTCFG /rebuild [Enter] Iterates through all Windows installations so that you can specify which installations to add.
The rebuild process will step you through a number of steps depending upon how many operating systems you have on the computer and how the computer is setup. Below is a listing of the common steps you are likely going to encounter.

* Prompt for the identified versions of Windows installed. When you receive this prompt press Y if the bootcfg command properly identified each of the Windows operating systems installed on the computer. It is important to realize this command will only detect Windows XP, Windows 2000, and Windows NT installations.

* Prompt to enter the load identifier. This is the name of the operating system for the boot.ini. For example, Microsoft Windows XP Home users would enter "Microsoft Windows XP Home edition".

* Prompt to Enter OS load options. When this prompt is received type /fastdetect to automatically detect the available options.

Once you have completed all the available options in the rebuild and are back at the prompt type exit to reboot the computer.
Description of the Windows XP Recovery Console
Windows XP herstellen naar een “net-geinstalleerde” versie, met behoud van data.

Thanks for the advice. In the meantime I re-installed without formatting (keeping configurations), since the problem is apparently not in boot, mbr, but a bit further into the system. At the moment I have a working version, except for Internet Explorer and email programs that depend on that. Other programs that use internet directly are okay. I have an install of Internet Explorer 7, but that refuses to load without SP2. I can't downoad SP2 (no Internet Explorer), also not on my laptop which uses Vista and for which MS decides that I don't need to download XP's SP2...

But before attempting anything else, I will save some more data, and maybe do a clean install on a (then) empty partition. I am transferring most of my actual work to my laptop, but miss having access to some old emails.

And as most of you, I don't allow automatic updates, but keeping up to date with patches usually helps, and in the worst case in the past I could use a recovery point.

(English)
IE and Windows XP Service Pack 3
we strongly recommend uninstalling IE8 Beta 1 prior to upgrading to Windows XP SP3 to eliminate any deployment issues and install IE8 Beta 1 after XPSP3 is on your machine.


(Dutch)
XP SP3 maakt verwijderen bèta IE8 onmogelijk

donderdag, 15:27 uur
Microsoft waarschuwt gebruikers van Internet Explorer 7 en Internet Explorer 8 Bèta 1 dat ze na installatie van Windows XP Service Pack 3 de browser niet meer kunnen downgraden.

(English)
XP SP3 cripples some PCs with endless reboots By Gregg Keizer, Computerworld
Windows blogger has tentatively identified XP SP3's endless reboot problem as involving only machines using processors from AMD

(Dutch)
XP SP3 laat computers eindeloos rebooten, Door Martin Gijzemijter
Het installeren van Windows XP Service Pack 3 veroorzaakt bij sommige computers een probleem, waardoor het systeem steeds opnieuw opstart.

sorry this was the only way that I knew of:
How-to repair Windows XP, How to Perform an In-Place Upgrade
Windows XP herstellen naar een “net-geinstalleerde” versie, met behoud van data.

Quoting Staid S Barr:

Quote:
Giga,

If you use that, also all the settings are lost.

I did make a clean install on a different partition, but don't know how to access old settings and directories. Even if I use the same username and password, I don't get access. Fortunately most of my data are safe, but 6 years worth of programs installations, upgrades and so on may need to be redone. And many of the downloaded files are in an inaccessible directory too...

How stupid do you have to be to attempt a second reinstall of SP3...?

I'll keep the old partition. Maybe I will find out how to do an upgrade. But I fear an attempted Repair from the CD made matters worse. First there where endless reboots (with a green message screen flashing by), after the "Repair" a blue screen flashed by (something about winsrv or winsvr missing) and the system turns itself off. That's one way to solve the reboot problem!

SP3 failing on some systems is tolerable, but not having a rollback option is criminal neglicence on the side of MS.

Microsoft is offering free unlimited support for XP SP3 installation problems until 14 April 2009. See here.