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.

The Java version that you'll link to from that post is now Java 6 update 3. Some people have had problems with the latest Java versions, so it's up to you if you want to try that one or not. I'm using it & it's fine for me.

This older version of Java has worked better for a lot of people. 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