Well, Java/
Java EE[
^]/
JavaFX[
^] has a lot of features you will find useful - so I think it's a good choice for an interactive "online tutor" project. And even while we may hate to admit it,
JavaFX[
^] currently has more visualiztion features than SilverLight, but that probably isn't going to last as SilverLight 5 introduces a decent 3d api.
Still, Java EE, has
message driven beans[
^], and
publish/subscribe based messaging[
^] - in a securable envirinment - so concentrate on just leveraging the features of
Glassfish[
^].
Best regards
Espen Harlinn