Weird, - although it shouldn't surprise me, if you are using apple's lame excuse for a java runtime environment. The setModal(boolean) method, your MRJ obviously does not know should work, since it does seem to know the java.awt.Dialog class.

Unfortunately there is no workaround - apart from modifying the source or copying a limewire.props file (from a someone successfully running LimeWire on MacOS).

By I have my doubts that LimeWire will run, - no matter what you do.