There are lots of hacks for Leopard installers, some are borderline impossible, while others are DECENT.
A well known one is JaS OS 10.5.1 but it still has lots of hardware compatablity bugs and can be a little tough to install.
EFI-X makes a USB dongle thing that can supposedly help install OS X on a generic PC with the normal retail disc. It even handles the drivers. Do a little research on these two things if you're really into it.
...Otherwise, it's kinda not worth it.