Compile Module for Atmel ARM920T

Hello!

I have the following system:
- Target System: Atmel AT91RM9200 (includes ARM920T) with Linux 2.6.14
- My computer (where I compile the software): Ubuntu 9.04 /
Crosscompiler: arm-linux-gcc-3.3.2

I successfully installed the crosscompiler and I'm also able to compile
and run a "HelloWorld" on my target system

Now I want to learn about dynamically loaded modules (with insmod). So I
want to make a module for my target system.

I heard a lot about the kernel source-code tree which is necessary to
build a module from kernel 2.6.x on... But what do I really have to do?

Do you have some good tutorials and an example what I have to do for my
configuration?

Thanks!
Michael