you have to download a bootdisk from www.bootdisk.com
and format the unallocated space to FAT32.
boot with the floppy, type "fdisk" then follow instructions
I sould install 98 first and then Xp because it could overwrite your XP bootsector. I am not sure what happens if u install 98 but probably XP won't boot afterwards. You can try to hide the XP partition before u install 98 though, it MOSTLY worked for me.
If one of those operating systems isn't working afterwards u might wnt to try out a bootmanager like PQ Bootmagic or bootstar bootmanager.
But its way safer to install 98 first and then install XP on the second partitions.
BTW, u can also use the XP disc to format the unalloacted space.