How to install new OS on a "downed" system.?

I need someone to give me some insight on how to install win 98 on a desktop that previously had win xp on it. simple enough, right? but the xp was corrupted (win32/sys/Ntfs) doesn't allow it to boot up at all. I can only get to the setup menu that you push DELETE to get to before the windows logo comes up. I have a bootable win98 disk, but it doesn't seem to be working...I need serious help here, guys. Thanks!