It worked!
Both my new systems are built now. I did not perform a clean OS installation on either computer. One computer was transformed form an AMD-Abit KR7A-R to an AMD Barton - Abit nForce board; the other was from an AMD - Abit KX7333-R to an Intel P4 - Abit IC7. Those are pretty radically different setups.
Here's how I did it:
1) remove/uninstall nearly all drivers and devices via Windows' "Add or Remove Programs" and Device Manager
2) used RegCleaner to remove remnants of device drivers (where possible)
3) shut down system
4) disassemble
5) rebuild (using hard drives fresh from the previous configurations)
6) reset CMOS
7) start-boot to CD
8) install WinXP in "Repair" mode
9) as soon as Windows is up, install all device drivers from the motherboard CD
After steps one through nine were executed, there were still leftover, unneeded devices, such as Highpoint RAID and Highpoint RCM. Windows was unable to remove everything, as some removals requiring rebooting on the original machine.
Both before and after rebuild, in Device Manager, under view setting, select "Show Hidden Devices"
Before I did all this though, I backed up everything to spare hard drives using Norton Ghost. I also used the Files and Settings Transfer Wizard to back up Windows and programs settings. Email folders were also exported or archived depending on clients used.