Its the same socket type but I think you have to stick to the Clovertown series. The highest I believe you can go is a Xeon X5365 which is a Quad-Core at 3GHz. The processors you can upgrade too are the same that you can do in a Mac Pro 1,1. I went from my dual-core 2.0GHz 5130 to two quad-core 2.66GHz X5355. I've been looking to upgrade my Xserve as well and I'll probably do the same as I did in my Mac Pro.