Not sure then. You could check these links which apply to your model graphic card: 1. Radeon 9800 Issue 1, & 2. Radeon 9800 Issue 2

Other than that, all I can think of is swapping java versions around. 1.5 to 1.4.2
There's also the Java 1.6 beta which has had good reports, but you'd need to uninstall all other versions of Java before you could use it with LW: http://java.sun.com/javase/6/download.jsp JRE "Offline" version which is a 15.72 MB download.
LW will not use Java 1.6 beta unless it's the only version running!

I presume you played around with the graphic card settings.