1. the win98 installation CD;
2. win98 start-up floppy disk;
3. drivers (unlike XP, win98 includes much fewer, if any, drivers) CD.
To format, just insert any system CD or anti-virus CD or floppy disk and to start the computer in DOS.
Then, type:
format C:
After completion, type; win98 setup (or setup win98) with the floppy disk inside.
I did it long ago and may be wrong. After I reinstall win98, I took long time to search the drivers to make the computer work properly. Really painstaking.