100% concur with Jinx about purchasing RAM from Apple. However, from what I have read, with the mini being, errr, mini, things can get a little tight and fiddly. I am able to purchase Apple products thru an employee discount scheme and therefore can get the extra RAM for a reasonable price, otherwise, I would have followed Jinx's advice.
I think I am going for a Core Duo, 2GB RAM, 120GB HD with superdrive, all hooked up to my 52 inch HDTV and 5.1 Amp. All to play music...!