For ATI card users there seems to be an issue with some of the catalyst control centre versions, AA and Java.
I found that disabling AA completely in the ATI CCC advanced settings allows me to load up this game and other Java based games.
If this helps any of you with the same issue I had leave a comment to get this added to the sticky as I found this info hard to find.
I would strongly recommend you update your drivers then, or at least re-install your current ones. On various Radeon based boards (4000 though 6000 boards) I have used this is a non-issue. On top of that, the AA setting in the CCC only affect DirectX based games, not OpenGL games like Spiral Knights.
There is confirmed texture oddities with Catalyst 11.3, but using Catalyst 11.2 there should be no driver created problems.