An awesome little box. Installation is very easy, I've tried it with both Windows XP and Windows 7 and both are excellent.
Been using it exactly how it was made for; with a mirophone in the XLR and a guitar/bass in the 1/4 jack socket, just make sure you select the right input source in your recording software! The drivers that come with it allow for extremely fast playback even using live effects software such as Guitar Rig.
The variable gain on the inputs is extremely useful too, since no two guitars or mics are going to be the same volume output.
I couldn't be happier with my M-Audio FastTrack!