// rdiskXsX: you have to know the proper partition names and replace them with X.
In my case, it would rdisk1s1, first HDD, and first partition, on which leopard has been installed, which needs to be made bootable //

1 -> Launch DVD
2 -> At boot prompt, type -s (single user mode)
3 -> Type:

fdisk -e /dev/rdisk0
update
f 1
w (y)
q

4 ->
cd /usr/standalone/i386
./startupfiletool -v /dev/rdis0sX ./boot (X is your partition)

5 ->
mount -uw /
mount -t hfs /dev/disk0sX /Volumes

6 ->
bless -device /dev/disk0sX -setBoot -verbose

7 -> reboot