What this might mean is that he installed Windows after Ubuntu, and can no
longer boot the latter. You might verify what I'm about to say from some other
source, because I haven't done it in a long time. Use the Ubuntu disk to boot,
and in a terminal window reinstall GRUB:

>root (hd0,x) (the partition in which GRUB is installed)
>setup (hd0)
>quit

You should be able to boot into Ubuntu. If Windows wasn't installed before,
though, you'll have to add a stanza to /boot/grub/menu.lst to make it show up in
the boot menu.