Radeon HD 3870
Windows 7 64bit
4GB DDR2 Ram
I had no problems with my video card until I installed the plugin java for the game. I can still play this game normally and it works. But after installation of this, it keeps crashing while I watch a movie or play another game like Left4Dead 2.
After I uninstalled Spiral Knight and Java, all problems disappeared.
Try it just the Java install. I don't really see how Spiral Knights should be killing other software when I don't believe it runs anything when it's not fully running.