Add a Single User mode entry in Grub bootloader.

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