Pop in your startup floppy disk then boot up pc. It should start booting from the floppy. When it's finished loading what it needs just type format c: and that should be that. Make sure you put the space between format and c (this is assuming that your hardrive is the 'c' drive)
After that type fdisk to partition then cd d:\ to change to your cdrom drive then d:\setup to start the 98 installation.