Hi Senee,
If you're interested in making art contributions to UFO:AI, we'd be very happy to have you on board!
You'd be working mostly with me (I'm design lead and I do art direction as well). We generally have a loose way of working where works in progress are posted to the forums, so everyone can make suggestions, although only mattn, hoehrer, BTAxis and me have a say about whether or not something needs changing or is ready for inclusion in the game.
Or, if you'd rather work with me personally by forum PMs or other messaging programs, that's fine with me too. Just let us know!
Regards,
Winter