Slow VM Processing Java Applet in IE 5-6

We have a java menu applet used on our intranet to navigate the site. On some computers (speed, OS, software version not a significant factor), this applet loads quickly. Netscape loads this applet in about 5 seconds on all computers. IE users report load time in the 5-30 second range the first time they use the site after boot-up. Subsequent loads are instantaneous. Users experiencing more than 10 second load time are complaining. Why is IE slower, and is there a way to speed up the Java load time? Users are mostly on Windows 98, 2000, and NT.