Get a rescue CD (e.g. from here:
http://rescuecd.sourceforge.net/download.html), boot your computer from it, then login as root (if you use the rescue CD mentioned before, the password is
rescue, then mount your hard disk, chroot to it and set a new password for root:
Code:
mount -t auto /dev/hda1 /mnt
cd /mnt
chroot /mnt
passwd root
Reboot your PC (don't forget to take out the RescueCD), and should be able to login as root.
tyler