Does not allow you to boot of CD, been a while since I had to deal with that on something other than an embedded system. I will question the wisdom of using 'buntu (even XCFE based) something that old though.
Three main ways:
rip the drive out and install a grub partition on there to do what you want using another system. Not pretty but I can deal with that.
use a loader disc (same idea as wakepuppy), been a while since I had to do this for something other than dos and before I start rocking in the corner at mention of himem.sys I will link to
Strictly speaking it is not exactly what you want but the potential is there.
chain a drive to do what you want. I am thinking CF to IDE here leaving the original drive free to do your bidding.