Try the tips here: Reduce the drag caused by LW
To disable ultrapeer capabilities in new versions of LW, 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 JRE 6 update 6. Remove any other Java versions installed (via Add/Remove Programs) before you install a new version.

If you have trouble with that latest Java version, try this older version.
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