What I want to achieve is to write a application on PC (WinXP) that will guide the user to do the following things:

1. Copy PDA application and associated files(File names are different from PDAs) from PC to PDAs(Around 80 PDAs).
2. After run the PDA application , copy files (generated by PDA application) from PDAs(Around 80 PDAs) to PC.
3. Assume the PDA shall be connected with PC via USB cable or cradle.

I'm new to PDA programming, so I have few idea about where I should start with, for example:
1. What programming language shall I use? VC++, J2ME or something else?
2. What development evironment or tool shall I use?
3. Is it possible for the PC application to be run on other platforms, such as Linux,Mac and Windows Vista?
4. Is it possilbe for the PC application to support all PDA hardwares with different PDA operating systems, such as WinCE?
5. Anything else I need to know?

Any one can give me some guidance? Thanks a lot!