I had the "Disk write error" with my hard drive and Windows 98, and it turned out to be that the IDE cable (The big wide grey one) was loose. Before going and spending out on a new hard drive, consider these things:

1. It could just be a loose cable, so open up your case and check.

2. It could be a virus, in which case you will need to use a program called "FDISK" instead of using "FORMAT". You will need to use this program to delete the primary partition in the hard drive and create a new one, then format it again and have another go at installing Windows 98.

3. The worst possible explanation is that the hard drive may just be damaged or is failing, in which case you should buy a new one.

cheers

Sharpshooter