If u still have problem with booting in leopard here is my advice for u all.
I was trying to boot leopard but no success. I was using Tiger to boot in Leopard and try this thing then:
1. Format hdd or partition where was tiger and Leopard
2. Install tiger becouse boot loader is working on tiger and before u start to tiping your name and password restart
3. Install Leopard AMD 10.5.1 and go in safe mod after f8 us -x for safemod and remove GeForce and NV kexts
4. Restart and boot normaly in Leopard without DVD becouse Leopard have boot loader from tiger now and work's fine
5. If u boot without going in safe modthat is bether becouse i had to remove geforce and nv kext's to make it work

So this is my way harder but 100% work. I am not smart ass but just trying to help.
Good luck to us all.
See u soon.