If you have a widows startup floppy , go into bios and change the boot sequence to a/c, then place floppy in drive switch on machine, type, format c:
Thats all there is to it, bare in mind all every thing on your Hard idsk will be gone.
If you want to do a clean windows install,put win98 disk into cd drive, again boot from the floppy, and just type setup.
good luck