I believe that your system can run all the newest leopard versions (10.5.6, 10.5.7, 10.5.8) but you have to:
1)Adjust your bios correctly
2)Select the appropriate patches from the installation dvd

I think that you have to be more specific if you want to receive more help and not some general tips. You can also make some research through the net in order to find some people who have a working leopard installation in a system close to yours. As you can see my setup is entirely different than yours,so I cannot provide you more specific information for the time being

About my system:
Motherboard: Supermicro H8DAE-2 with nVidia MCP55 Pro chipset which supports up to two Six-Core AMD Opteron 2000/8000 processors
Super Micro Computer, Inc. - Aplus Products | Motherboards | H8DAE-2
Processor: 1x Opteron 8214 (for the time being) :-)
Ram: 4 GB Samsung DDR2 667 Registered ECC Unbuffered
Graphics Card: Nvidia 9400 GT
I also have two SATA hard disks, 120 GB and 640GB , a Sony IDE DVD reader and an Optiarc DVD Recorder.