OK, in Ubuntu, type (in terminal):
# sudo mkdir /media/slax
# sudo mount /dev/hda5 /media/slax
OK, once there, navigate to your /media/slax/boot directory. In there, you said there was a vmlinuz file - take the version number of that. In fact, copy the whole name. If there is an initrd, then copy that too. Then, in your menu.lst, put in the following entry:
kernel /boot/vmlinuz-version root=/dev/hda5 vga=792
initrd /boot/initrd-blahblah.img #There should be one
Does that work? Hope it does!