Here again, are a number of ways to make a bootable external disc. Here is how I did mine. I loaded up my Leopard disc and rebooted. Then started disc utility and Making sure what Mac you have and using the right partition map.
I use Guid for my intel imac.
Then Partitioned into two volumes; the first I called leopard and the second I called time machine-for my backups. Works great. I used 50mb for 1st and 247mb for 2nd. Now I have a bootable drive and backup on the same external hard drive.
Here are some links to other ways. First from Macfixit. If your not a subscriber, better save to a pdf-while it's free.
clone of leopard
Here is another two items I got from a google search. I'm sure there are more. JonL
booting an intel imac from an external drive
creating a bootable firewire disk