My chipset is nvidia MCP55Pro(=nForce professional 3600) :-) Right now I'm using leopard 10.5.8 which is rock-stable on my system. Some nForce SATA controllers are supporting AHCI mode, and some others(like mine) don't. I'm using AppleNforceATA.kext and a slightly modified IOATAFAMILY.kext and everything is fine.If your controller supports AHCI mode I think that you will not need AppleNForceATA.kext. I'm also using NForceLAN.kext which is also working perfect with my dual on-board lan.
You have to find the right kexts for your system in order to make a succesful leopard installation. I had to install leopard many times in order to find the most appropriate installation options,as I hadn't found any info provided by someone who had successfully installed leopard on an opteron serverboard.