Hmmm. The new preview release (http://www.spotify.com/download/previews/) has a better chance of working, but still doesn't officially support tablets. If you have a 3G Xoom with a data connection then you should be fine. However if you have a non-3G tab then you might find you struggle to get it to run online - see various threads on this board about being constantly offline.
---------------- Listening on Windows, Android and Sonos. Tweeting it at @davelicence