How can you create MW2 Mods?

Hey guys,
I was wondering how somebody can create MW2 Mods (for MW2 Liberation)
I really want to know that so I can create my own mods..

Is there any program to do it or you have to work out the code?

Thanks a lot

You have to work out the code.
the easiest way to start learning is probably this:

Get a clean _rank.gsc
http://www.mpgh.net/forum/323-call-d...ollection.html

Then download a mod.
Note that some modders 'arrange' their code in a very messy fashion, which makes it very hard to read let alone learn from.
So use a mod that is somewhat organised. I suggest looking at azumikkel mods, or mine for instance.
Example:
http://www.mpgh.net/forum/308-call-d...d-updated.html

Now open the _rank.gsc from this mod and read the code and try to 'understand' it.
It's all very logical one you get the hang of it.

You can now start putting your code in the clean gsc.
once you get the hang of it, you can look for in depth tutorials on functions and codes.

Good luck! Have fun