You can run 3 virtual machines on a quad core, with 1 core dedicated to each VM and one for your home OS for best performance. I doubt you'll be able to get by with just 4GB of RAM though (you'll want to allocate AT LEAST 1GB of RAM to each VM, 2GB is better). And that's just with the VMs with only core processes running. Don't get an i3 like that one poster said. That would be a waste of money. An AMD FX cpu seems like it would be perfect for you since you're on a budget. Also, get as much RAM as you can afford. Your current set up should run it, albeit probably not that well.