Is art games? Because if not, then it can fuck off.
Also, my genitals are both a game and a work of art.
On a less flippant note, I don't think there's any single universally agreed-upon definition of game, and there certainly isn't one for art. I don't think there ever will be, for either of them. The best attempt I've seen to come up with a series of different definitions that go some way towards a coherent whole is probaly the book "Rules of Play - Game Design Fundamentals":http://mitpress.mit.edu/catalog/item/default.asp?ttype=2&tid=9802
It's quite a big book, but it sort of covers the tip of the iceberg at least.