Hey! Have a look at this! http://www.insanelymac.com/forum/lof...p/t158685.html
This should do the job.
I've never installed 10.5.4 so I'm not sure,but for 10.5.6-10.5.7 and 10.5.8 the driver installer isn't necessary. Anyway,the driver is for leopard 10.5.5 or greater, so don't download the file! Just follow all the other steps in order to make an EFI string!

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.