A nice article on Xen can be found on LinuxDevCenter, it's a quick guide to get you started on Xen. Indeed interesting things are happening in the virtualization area, and OSS is delivering very good products as usual. If you do not have a spare PC or don't want to mess around with your current install, you can use QEMU, it will be included in your distro in most cases. QEMU is neat, and is not just another VM, it has an edge as it can emulate complete architectures. Run PPC, ARM, SPARC and others on your host. Try out PPC Linux, or find out how well Linux works on a 64bit machine, all from your current machine.