All you need to do is add 'single' to the end of any bootloader entry to make it single user. So what you need to do is edit the /boot/grub/menu.lst, copy one of the entries, and all 'single' to the end.
gksudo kate /boot/grub/menu.lst
take the 'kernel' line and add 'single' to the end. Like this:
kernel /boot/vmlinuz-2.6.27-11-generic root=UUID=3699a36a-dd96-4186-8028-43776214c01e ro quiet splash single