First look to see that IW is using the Java plugin, type about
lugins in the URL bar.
Java(TM) Plug-in 1.6.0-b105
File name: /usr/lib/jvm/java-6-sun-1.6.0.00/jre/plugin/i386/ns7/libjavaplugin_oji.so
Java(TM) Plug-in 1.6.0
Should be there, if not its not installed correctly, just do a apt-get packagename -reinstall. Or try to use dpkg to reconfigure java.