yeah, you need to make a link to the plugin.
lrwxr-xr-x 1 jule users 56 Nov 12 2004 /home/jule/.mozilla/plugins/libjavaplugin_oji.so -> /usr/local/java/jre/plugin/i386/ns7/libjavaplugin_oji.so
This is actually the blackdown JDK plugin.
I have it in my homedirectory. Make sure you use the ns7 one.
Appletviewer might not be in your path. It does come with the standard JDK from Sun.
/opt/sun-jdk-1.4.2.09/bin/appletviewer