Thanks to all who replied. Now I have some confidence about going ahead.
Jeff said:
I am replacing a dead motherboard with the same model. Can I expect my XP
install to boot, and if not, will a Repair install destroy any data other
than restore points, i.e., will my email, documents, etc. remain intact?
If it is the same model you may get away with it, If it does not boot
freely straight off though, do the repair.
Set the BIOS to boot CD before Hard disk, then boot the XP CD, start
Setup (do not take 'Repair' at this stage), then after the license
agreement take 'Repair Installation'. This will retain your existing
software installations and most settings. But Updates will have to be
run again, especially SP1;
It is important to activate the basic XP Firewall before you ever
connect to the net to get the patches, so as to be protected against
things like the BLAST worm.
This should retain your activation status, though if you have never
registered you may have the setup suggest it now (don't bother). But
you may nevertheless find (either way) that you have made so many
changes that you need to activate again by phoning in. See
www.aumha.org/win5/a/wpa.htm on what items affect that