I'm having trouble again. I don't know what I do to deserve it.

I decided to give up on 98SE and get XP, for my other computer, not this one.
XP would NOT go in to the P4/2.6, so I formatted, and now I can't get 98SE to go back in either. Nor 98. Nor ME. They get halfway in and then start crashing.
I have formatted, including 3 deep formats, (Zero fill, as Seagate call it.) Tried reinstalling between, no good, and have to format again to get out of it because Windows won't load, even from A:boot.
The best I've had is "Preparing to run Windows for the first time." Crash. "General Protection Fault in module USER.EXE at 0007:1790. Jammed.
I've tried installing all three OSs direct from the CD drive, and got these error messages: (With XP)Corrupt file(s) msnp32.dll vnetsup.vxd dfs.vxd vredir.vxd   
(with 98SE) VGA.SYS corrupted.
(with 98) Windows Protection Error.
I've flashed the BIOS by removing the battery, and then resetting the defaults. The BIOS is the current build #. I've removed the cards and the SCSI port card-which would need an updated driver anyway- and formatted.
The motherboard is an ASRock P4S61, nothing unusual. No cards in it now. HD is a Seagate 40gig, their own formatter says it is fine. 512 of ram(that's new), Creative DVD reader, CD burner, Zip-drive, and nothing else now. It was working well until I tried to install XP. I did try to install with the SCSI port in, and XP said I would need another driver for that and the modem, but it didn't seem fussed about it then.

I have downloaded the BIOS (for that computer)on this machine, but I don't know how to get it onto that one, and have received stern warnings anyway.
XP did go into THIS machine flawlessly, and then out again because I want it in the other one. However, now I'll settle for whatever I can get, as long as they're both working.

I'm out of ideas, and open to suggestions. Pretty please.   Chris.