Found another article (with screenshots) on Linux KVM Virtualization Performance. KVM is the new kernel model virtualization technique, which allows you to run other OSs through a kernel module, very similar to vmware or Xen, but without the need for a modified kernel (Xen) or non-free application (vmware) and with increased performance because of how close it can run to the kernel (a la Xen).

Only sucky part is that you need a CPU with VT technology (either from Intel or AMD) built in. Of course, this means just about any CPU you buy these days, but not necessarily older ones.