A blogger who goes by the name of Smash has posted a how-to video on disassemble the Mac mini. With Apple requiring Apple-authorized service centers to do all RAM and hard drive upgrades, the movie shows die-hard do-it-yourselfers how to crack the case.
We should note, of course, that cracking the case is likely to void your warranty. As Smash noted, however, a MacCentral report by Dan Frakes said that Apple had told Macworld magazine that you can do it yourself without voiding your warranty "unless you break something when you open it."
TMO has not confirmed that, however, and we strongly advise you to try it at your own risk.
You can see the movie and Smashis accompanying notes at Smashworld.