Dave
During the initial installation XP configures itself to suit the hardware in
order to provide a more stable system. Because of this a major change in
hardware can cause problems.
**** If you have a XP installation CD ****
You should always back up any important files in advance of a hardware
change.
Many users, myself included, prefer to do a full clean install after major
hardware changes as you describe.
The alternative, and equally valid option, is the repair install (also known
as an In-Place Upgrade).
See following Knowledge Base article for details. Pay careful attention to
the possible loss of data links in the MS article.
How to Perform an In-Place Upgrade (Reinstallation) of Windows XP
http://support.microsoft.com/default.aspx?scid=KB;EN-US;Q315341&ID=KB;EN-US;Q315341
After doing this you may need to re-activate your installation of XP. If it
has been more than 120 days since you last re-activated you should be able
to activate over the internet, otherwise it will require a short phonecall.
After the repair install you will need to re-install any XP service packs
and updates that are not included on your XP Installation CD, but you will
not need to re-install any applications.
Hope that helps
Pete