I'am forced by my company to upgrade an old Java application. The situation is, that an signed applet calls several servlets (running on Tomcat 4.x or 5.x) over http(s).
In former times both, servlet container and applet, were using jre 1.4.1.x (The servlet container was ServletExec, so a jre was sufficient).
Everything was working fine, if the client was using the 1.4.1 jre. But on later versions (1.4.2.x) the whole Applet-jar was downloaded from the server per user interaction, whats definitly not acceptable as customers still using isdn or nowadays umts.
You can specify the java version in the converted applet tag. I can't remember exactly but used to do this in the past. Search for HtmlConverter in java.sun.com and you'll find some documentation about applet (static and dynamic download...)