yes it is possible, but you"ll be limited to some old ubuntu version as the pegasos is not supported anymore (if it ever was).
You'll find some boot and netinstall images here : http://genesi.hu/ubuntu/

AFAIK debian still supports the pegasos.

About bootmenu, all you need is to add an entry with the boot image name followed by the path to your root partition.
There are some tutorials that are a bit old but that could help on the web.

here is bootmenu http://aminet.net/package/util/boot/bootmenu (read the manual)


[ Edited by SoundSquare 29.06.2011 - 14:05 ]