I have an ASUS P5N-EM HDMI motherboard. Currently, it's using an oldish P4 cpu. Works fine.
I just received a spankin' new Core2 Quad Processor Q8400 a few mins ago. Unopened, in the box.
I have no idea if this cpu will work in my motherboard. My motherboard is a Socket LGA775, though. I'm running the latest BIOS (for my mobo) which is version 4.01. That said, I don't think the CPU is listed on any documentation. I'm worried that it won't work .. and if so .. why would that be?! The mobo is around 8 months old, i think.