Fuck, you can get a Pentium D chip on the cheap that supports virtualization.
http://shop.ebay.com/?_from=R40&_trksid ... CategoriesOr do it semi right and get a C2Q 8400 or higher. When running hyper v you are not necessarily worried about proc speed as you are the amount of cores you have in your server. If you want some raw numbers I can get some reports on our R905 cluster (4 servers, each quad quads) and our 2950s (2 servers each dual quads) and you can see the difference in performance... If you upgraded to a C2Q, have 4gb of RAM, you could feasibly run 4 guests in hyper v. Though it may feel slow because you are bottlenecked by your hard drives(s). The amount of spindals matter too, 4 guests - a SQL server, exchange, file server, and dns - each shares the drive(s), exchange and SQL are both heavy on IO. Where as in a physical enviornment, each server would have typically 3-5 drives in a raid 50 configuration, or be attached to some network storage array.