How common is browser support for java applets? They work fine on some computers, but not on others - mostly when using IE. Is this a problem with people using old browsers, IE, or something else?

afaik ~ they are commonly usable in all main browsers.
anyone using a really really old browser that does not support them is probably already used to not being able to view half of the web as other things would not be supported as well.

That's what I thought, but I am still getting complaints that a menu applet that I have doesn't show up. It is located at www.garagetowntexas.com/menu.html. Is there something wrong with that specific applet?

looks ok to me in firefox2.
looks ok to me in ie6.
ie makes me click on it first before using the menu... grrr... ie...
no validation errors or warnings.