I'm not sure if anyone has figured this out, but I recently setup a 1.6A Northwood/P4B266-C setup, and I encountered the no post with a MS USB mouse attached issue. I easily got around it by using the PS2 adapter, but I really wanted to use it via USB. I figured out that one of the initial tests the board does when it's first booted is what causes the hang. If you connect the mouse via USB after it says the "PNP Initialized" or something, right when it's finding your IDE drives, it will work like a charm. As an alternative, you can wait until it boots into the OS, then connect it. It seems to be an issue with the boards initialization sequence. Just thought I would let you guys know if you are having this issue.. 🙂