The java-virtual machine built into NS4.x on Unix is very slow, so on Unix you are advised to use a java plugin (e.g. from Sun, Compaq) or run it directly using java appletviewer.
Please tell me about other browsers / JVMs
Note if Netscape exits reporting "bus error", this is due to a netscape bug applying to all java applets, which you can fix by setting the font path to include 75dpi fonts.