When I write applets for TINI, can I use the classes in JDK1.2 rather than just the classes provided by TINI, since the applet will be running on the client machine?

Applets served up from the TINI to the client are just binary files (bytecode) which will be executed on the client. Since these applets will run on the client, they can be written with any version of Java that the client supports, including JDK 1.2.