From what I can ascertain, your model was released in 2006 & is not an intel 64 bit machine. Since you are using Leopard which only has 64 bit Java 1.6 & not 32 bit java, your machine will not be able to run LW 5 unless you upgraded to Snow Leopard OSX 10.6 which has both 32 & 64 bit java.

So for now at least, you will only be able to run LW 4 by looks of things. To downgrade to LW 4, you will first need to remove the install limewire.pkg file from receipts folder. See more about this here: http://www.gnutellaforums.com/mac-os...ck-lw-4-a.html