Are you using DOS or UNIX or AMEGA .. what the heck .. are we supposed to guess? The forum rules are simple & are there for a reason so we don't play guessing games & waste a lot of our & your time.
Try this approach: http://www.gnutellaforums.com/333278-post2.html

Edit: for mac, please specify your OSX version, and check which java version you have which can be found via the Java preferences: Setting up Java for Leopard (see 2nd image). You need Java 6 (preferably 64-bit but if you have 32 bit that will work.)