When I start it, it goes thru the 98 boot screen, does the diagnostics, then brings me to a dos prompt
When you say it brings you to a windows 98 screen and then the diagnositcs and then to DOS, are you getting the 98 splash screen? If so, the drive may not be fully formatted. Or are you using the win98 boot disk?

Also, go into the BIOS on the computer and see if you can set the cdrom as the primary boot device. If you can, set the device as primary and boot the pc with the cd in and the boot disk out. The cd should autostart.

Depending on the age of the pc though, you may run into some problems. Older cdroms do not support ATAPI and therefore will not boot. Also, some older MOBO configurations may not support the boot to CDROM. Then, you have the normal hardware requirements of the application.

Regarding the unmountable boot device. Make sure that you have the boot configuration correct in the bios. If you are still getting the error after checking the BIOS, download the harddrive utilities from the manufacturer and use it to format/check the disk for errors.