The longer answer is: most of the time you'll want to do this kind of thing, you probably want to use server-side JSP's (rather than client side applets). Honest!
'Hope that helps .. PSM
In any case, you'll need some external .jar - and you'll need the client to be able to install it on their PC and integrate it with their browser's JRE - in order for it to work. And if the client uses Firefox and IE ... they'll probably have to install and configure twice...