You can also allocate more memory to the Java Virtual Machine/Runtime environment. Yes, that's right folks, it seems Apple didn't tell the "whole" truth about OS X's memory management, at least when it comes to Java apps.

First of all, make sure you've quit Limewire before you try this out. Right click(or option click on the Limewire application icon, and choose "Show package contents" from the list. Then go into the Contents/Resources folder and find the file called "MRJApp.properties" and drag a *copy* of it to your desktop for safe-keeping. Then take the "MRJApp.properties" file and drag it onto TextEdit's icon in the dock.

Find the following lines and change them to whatever you wish:

com.apple.mrj.application.gc.max=64M

com.apple.mrj.application.gc.min=2M

As you may have guessed, these represent the maximum and minimum amount of RAM that LimeWire will be able to have. As these defaults are quite low, I've changed mine to 200M and 64M. M=MB's of memory.
So, my first line looks like:
com.apple.mrj.application.gc.max=200M

and so on...

Then just save the file and Start LimeWire up.

Hope this helps....