I've just had a problem with Wyvern not installing properly on Mac OS X 10.5 Leopard. I tried a few things and it seems that there's an issue with Java being 64bit and the Wyvern install not working properly.
If you have problems, try using java in 32bit mode. To do that use Terminal and type the following:
java -d32 -jar ~/Desktop/install.jar
You need to replace the last bit with the path to the install.jar. Mine just downloaded to the Desktop so I used that in the example. You can get that from the universal download part or here:
http://www.cabochon.com/downloads/je...ne/install.jar
HTH