|Well, you need to get into the bios and check/adjust the boot order. For the Dell it's probably F1 for F2. But the manual should tell you for sure.|
Then set the drive you're trying to boot from as the first device. Save and exit and reboot.
If you're using a 98 floppy bootdisk then choose cdrom support from the menu. Watch the text lines on the screen. The last few that load should tell you the drive letter it's assigned to the cdrom. Then, since it sounds like you haven't formatted, at the a:\> prompt type format c: and enter. When it's done type X:\setup and enter, where X: is the cdrom drive letter that showed on the screen when you booted with the bootdisk.
I guess it's pretty much the same procedure if you boot from the 98 cd. But when you run setup you may need to only type setup and enter.
Real men don't use AntiVirus; they just reformat