BobStern wrote: I learned on the MacInTouch website that US residents can buy Snow Leopard Server for only $20 (plus $4 postage plus sales tax) if you order directly from Apple by telephone (800-692-7753 or 866-254-8313).
You are misinformed, Snow Leopard Server is no longer available from Apple as a retail sale however Snow Leopard (client version) is and that is the one for 19.99 and is not legally virtualizable!
Have a look at: Mac OS X 10.6 Snow Leopard