How much "free" space do you have on your HDD? I'd suggest defragmenting it. And trying to keep total usage below 80% or else it will slow down.
Other things to try:
1. Uninstall all versions of Java. Install Java 1.6 beta "Offline" version which is about a 13 MB download:
http://java.sun.com/javase/6/download.jsp JRE "Offline" version
2.
Tip: Purge the Downloads Queue!
3. Keep shares below 2,000
4. Go to LW's menu bar, Tools>Options>iTunes>Sharing & disable this option.
5. After opening LW, let it settle for 5-10 mins before using. Don't use the Resume/Find Sources function on more than a few files at a time if you use this function, otherwise it will have a dramatic slowing down effect upon LW.
If still no improvement then try deleting your LW Preferences folder whilst LW is
closed; instructions here:
Point #2 & 3 in Fixes for Limewire (sample image included at bottom of page.)