Right now, the computer is trying to boot from the cd-device, and there's nothing to boot from in the cd-drive.
Open Nero, or some other burning utility, and burn the cd iso. DOn't just burn the file to a disk. It's a disk image, so what it'll do is extract all the needed data to a dvd.
If you don't have nero, you can search download.com for tons of free burners that will burn an iso. I don't know if Win98 came with a utility to do it.