I have the same problem as well. I had already installed Vista on my 1st partition and then formated the 2nd partition by Disk Utility and installed Leopard with Dual Boot option and Vista Bootloader.

When I have the 2nd partition active and without the dvd I get a "Missing Operating System" error, but with the dvd in I can normally boot into Leopard. If I have the 1st partition active (Vista) I can boot into Vista. I have entered with EasyBCD dual boot option in Vista Bootloader but when I choose Leopard from the menu I get "Chain Booting Error". If I try to boot with 1st partition active with the DVD in I go to the installation procees.

I am really stuck I have tested Leopard and works like a charm (VGA, Sound, Lan, even Time machine) but since I also use Vista I need a working solution for dual boot and without to format my drive and install both from the beginning.

If I install Leopard on another disk will this be an option for dual boot?

Any help will be highly appreciated