This robot is (in theory) perfectly capable of spinning on the spot, moving in any direction, and generally doing any planar motion you can imagine (although in some directions, such as straight forwards or backwards, you'd go quite fast but wouldn't have much pushing force). In practice, though, roller friction might make some types of motion difficult.
The math to make it work is actually pretty simple - I went over precisely that in my presentation at the FIRST Robotics Conference a few days ago. The presentation ("Omnidirectional Drive Systems") should be up on the FIRST site soon, but I've also uploaded it to CD-Media:
http://www.chiefdelphi.com/media/papers/1836
E-mail me or send me a private message if you'd like more detail on how to apply the theory to this particular robot...
EDIT: Actually, looking at the photo again, it looks like the three wheel planes intersect right at the front (back?) wheel, so no, full omnidirectional motion isn't possible. If the two angled bits were just angled some more and moved out further, though...