I recently bought a Sony Clie PDA which have Palm OS 4.1

How can I write applications for PDA? Which language do I have to use for that?
I searched for some help on web, but quite confused. Some say I need to write in C++, some say Java or some stress on LISP.

Which is the easiest way to develop applications for PDAs? Is there any free compiler etc. available?

Thanx