I found my problem, searching through bug reports at Sun's support site.

A patch to the Motif libraries, Patch # 108941-56, breaks the libXm.so.4 library, and will cause almost any Java program that uses swing calls to fail with signal 11 errors in libXm.

(Note: Signal 11 is the dread segfault!)

The only cure currently (Sept. 30th, 2003), is to back the patch out, and return to an earlier version of the libraries. 108941-49 is known to work, as I am running that version of libXm.so.4, and Limewire Beta seems to work well.

Sun does not keep old patches on their site, so if you can't find an old version of the library, or replace it by backing out the patch (i.e., no saved data from patches on your system), then you are hosed, and will need to contact Sun for either the older library version, or the older patch (108941-49).

Because this bug will cause huge problems for anyone running Java, it's likely that an updated patch will be released in a few days. You can pester SUN to give you a point patch to fix the problem, if all else fails.

Hope this helps someone else too,
Rockkeys