There is a couple of virtualization products out there. Besides Virtualbox fron SUN (link), we have VMWare (link) that offers the Player and the Server edition for free. These are great tools to run separate OS or separate “virtual” machines as server or clean environments. If you run several of them concurrent a 64bit version of Windows and more memory makes sense.
You can save quite some time if you either want to evaluate a product without installing or use without worrying too much about the installation process.
I have a openSolaris, Fedora9 and Windows2003 Server always on standby for testing, as well running a wiki, bugtracking,.. on it.