At the LILO or GRUB prompt, just add "single" to the boot line which will boot your system in single user mode.
If you use LILO do this:
LILO: linux single
If GRUB, press "a" at the GRUB boot menu. Move to the end of the kernel line and add "single" and press ENTER.
[ November 17, 2002: Message edited by: void main ]