I'm with Newf.
I did modified "Motherboard Upgrades" the last three times I built new systems, including this one, and like the previous two I will soon dump my C: system drive and reload WindowsXP Pro 32.
Doing an "upgrade" rather than a clean install, you always end up with drivers leftover from the previous install. Sometimes they can have a bad affect on operation. Like an nVidia 650i SLI mobo with discrete graphix trying to load Intel's igrfxsvc (integrated graphix driver) or Intel IDE.
I have two hdd, so Windows has its own primary partition/drive and all I have to do is re-format and reload, UPDATE, load system drivers, and go. There are a couple of work arounds for saving your user data/settings so you don't lose your established accounts and settings.
After loading Winders, you still have to visit Microsoft Update to re-load SP2 (if not already integrated/slipstreamed into your install disk) and all updates since then. It doesn't take too long over a broadband connection, if you have SP2 integrated. If you're on Vista, then I don't know.
A clean install is always the best way and is even recommended as a yearly housekeeping task.
Now, if I could only find my XP Pro installation disk... :?
TonyB.