Is the freeze only happening when you're actively downloading?

Try the tips here: Reduce the drag caused by LW
To disable ultrapeer capabilities in new versions, tools > options > advanced > performance. While you're there, also disable Mojito DHT capabilities...that might help as well.

The Java version that you'll link to from that post is now Java 6 update 4.

If you still have the same problem, try this older version of Java. Download
the JRE offline installer & remove your current Java before you install this one.
Archive: Download Java 2 Platform Standard Edition (J2SE) 5.0 Update 11