I am sorry about being late too, but for future reference, here is what you do.
Windows will ask you 2 (two) times when you boot with the CD if you wish to do a new install or a repair. Pay very close attention, this is how you do a new install over a previous install without wiping everything off of your drive......
Boot with your XP CD. When you boot you will see the option for "New Installation" or"Repair Windows Installation using the Recovery Console" DON'T DO THAT.
Skip that and go on to a new installation.
Windows install will run a minute, detect your drive, and discover that you have a previous version of Windows on drive "C".
It will show the drive with the XP installation on it.
At this point it will ask if you again if want to do a new installation, or repair the installation on drive "C". You will also see a message that says "WARNING choosing new install will delete everything on this drive" or something like that.
Choose AT THIS POINT to do the repair.
Be Careful!!! If you choose the new install again at this point, your drive will be formatted and everything is gone- *POOF*
Windows will run and appear to do a complete full install. What it is doing is detecting all your new hardware and rewriting all the tables for your new motherboard, chipset, etc. When you are done, all of your programs and settings will still be there. You will want to reinstall any 3rd party device drivers, like Video card, of course the drivers that came with your new motherboard, sound card, etc.
Any updates you have done from the Windows update site will also be undone, so be prepared for a long line of downloads, and waiting for all that to reinstall when Windows does it's first couple of auto updates from the site.
This WILL work. It is not as good as a new install, but definetly worth trying if you have a lot of stuff on your drive you do not want to spend hours and hours reinstalling. You will just have to see if in time everything works well, or if things are buggy and causing you trouble.
I have done it a couple of times now with 2 different motherboard upgrades with the same XP installation, and everything is still working perfectly.