The CD for XP is bootable. There is no such thing as a single floppy disk that can boot XP because NTFS driver support requires a minimum of 3 floppy disks.
Making a home made 98 CD that is bootable is impractical, because when your computer restarts it will boot from the CD and beging setup again. You'll have to change a number of things, but it is possible.
Many retail versions of 98 were bootable to begin with.