WinXP you said didn't you. your problem could just lie there win xp relies heavely on acpi managment now the evil lies in your Motherboards bios winxp tend's to have a thing for screwing up when you use an older version of acpi and knowing IBM who's bios revisions have been scary for years now this could be the case see if there is a bios update available for your model pc .
another thing you could try is setting your mem config in the bios to "by SPD"
otherwise try juggeling some of your pci/isa card's around (diff slot's) know that sounds funny but trust me it solves the prob sometimes it has to do with the irq assingment
Oh and btw SDK winXp doesn't have fdisk anymore now you have to fire up a recovery console and then type FIXMBR that will replace your MBR sometimes wise to run the FIXBOOT command too just to place a clean set of sys files