look, i was looking for the same information, found one topic.

as i can uderstand, the applet can be created in J#, the only difference from a Java applet is that a J# applet will require clients to have installed J# Redistributable and .NET Framework. here, have a look:

http://msdn.microsoft.com/en-us/library/aa290083(VS.71).aspx

here is explained how to convert java applets to J# web control library (that is the microsoft alternative to applet i think so). I'm happy finding this. :)

please comment if this is helpful. i'm interested in it.

Honestly the real solution to this problem is probably flash or silverlight.  If you're more comfortable with C# / java, go with silverlight.