An easy trick is to put a message like:
"You must have a Java-enabled browser to view this page"
...somewhere between the applet's start and stop APPLET tags. This way, if the browser does not support Java, instead of displaying the applet, the message will be displayed.
Here is an example (NOTE, however, that I left the greater-than and less-than signs off of the applet HTML because this forum doesn't display those symbols):
APPLET CODE = "uShopInputButton1.class" WIDTH=100 HEIGHT=35
You must have a Java-enabled browser to view this page.
PARAM NAME="id" VALUE="B00001"
PARAM NAME="name" VALUE="Romeo & Juliet"
PARAM NAME="description" VALUE="hard cover"
PARAM NAME="weight" VALUE="1"
PARAM NAME="price" VALUE="$ 19.95"
PARAM NAME="background" VALUE="white"
Note how I inserted that message just after the first line of the applet. This way, that line will be displayed only if the browser does not support Java.
On a side note, are you sure that the problem is that they don't have java enable? That is, make sure that the applets are not just getting cut off because of the WIDTH being to narrow. That is, make sure that you have the WIDTH of the applets large enough to work on both IE and Netscape (Netscape tends to require the WIDTH to be a little wider than IE....so just be sure to give a little extra room....10 or 20 pixels).