Please give us your system details as listed here
http://www.gnutellaforums.com/showthread.php?t=62652 Ram OS and Disk space are essential.
Updating your Java might be the problem and you should take a look at this
http://www.gnutellaforums.com/showthread.php?t=36420 but if you have tried other Java based applications, this is not so likely to be the problem