Windows

You Guys are my last hope, Microsoft was no help.
Have a one year old 64-Bit Computer. Rec'd my Vista RC1 32, DVD in the mail and loaded it on my 64-bit PC. Everything went perfect until I noticed that I couldn't use the Internet. After hours of research found out that the Motherbd maker has discontinued this Motherbd and there are no Vista drivers for the nForce-250 network controller for the on-board Nic card. So, I uninstalled Vista RC1 and tried to reinstall my Windows XP Pro and now I get an error that states "Error loading Operating System" just after "Boot from CD" and of course WinXP setup will not take off after the PC restarts from pre-setup.
Tried all the obvious tricks- Reformatted HD, fdisk from Win95 Boot floppy, even downloaded hard drive utility program to make sure the HD was clean but PC still also says another OS still resides along with Error Loading OS.
Haven't been this upset in years and fear I've lost my 64-bit machine to RC1.
Please, does anyone, know of a solution to get me back to WinXP since Vista dumped on me? I'll be very greatful.