http://osx86.wikidot.com/how-to-s#toc5
leave out steps 4 and 5 for mbr and see if that fixes it


Boot with the DVD and use -s at boot load.

sudo -s
fdisk -e /dev/rdiskX --->(X is the number of your HD, if you have only on its 0)
update
f X --->(X is the number of the partition where you installed Leopard)
w
q
reboot