Well I had this problem and tried several things, I wish I had tried the following first:
Go into the bios and change SATA settings from AHCI to ATA - from the thread "7B error at XP install" - http://www.tomshardware.com/forum/5231-45-error-install
I figure the disk was corrupt beyond some repair as I tried the same drive in another chassis and the problem moved to the new chassis, so that eliminated everything in the old chassis except the hard drive, though diags said everything was fine with the hard drive. So I decided to load Linux on the "bad" drive and it loaded and worked fine, went to reload XP and it had the same 7B error! Changed the bios as above and now happily loading XP, just wish I had googled the problem earlier and I would have tried the change before loading Linux and now reloading XP. Don't know if it will actually work, but worth a shot.