I remember the 487 FPU upgrade to a 486SX was really clever. The original 486SX was just a 486DX with a fuse blown to disable its FPU, the upgrade 487 FPU was actually a whole new 486DX which disabled the original CPU on your motherboard!
DON'T follow the hard disk instructions on that page, it's possible some drives have unmapped space because they've got failed platters that you definitely don't want to use, but more likely as other people posted, the partition tables on the drive are getting corrupted and although the table says there is lots of space, each new area is just pointing at the same physical space on the disk. That would be badTM!
Jim