Try this:
Make sure you have the latest Java installed for your Distro
Locate the Soundbank.gm, file OpenSuse uses /usr/lib/jvm/java-1.5.0-sun-1.5.0_update12/jre/lib/audio/soundbank.gm
for example.
Click on Settings from the Menu Bar
Select Configure TuxGuitar
Choose Sound Icon
Click the "Use Custom Sound Bank"Radio Button
Click the Folder Icon and select the directory containing Soundbank.gm,
If you have the Alas Plug-in intsalled you may have to deselect the Use Alas Plug-in Option from the Plug-Ins on Menu Bar