what kind of editors should i use and whare in JA base do i find C++ files

I'll start off....

C++ is a programming language. You need to learn how to do it in order to use it (there are books for sale, online sources, etc.) you also need a compiler (you can buy these and get them free some places, etc).

I imagine you'd find the files in the source portions of the SDK.

I don't program, so I can't help you learn, but good luck!

Try the editing forums (under "coding")...

If you don't even know what C++ is, then you shouldn't even be touching the code.

Note that while the actual game is probably in C++, the multiplayer portion of code is in C, so you should probably concentrate on learning that one. :)

I've done my fair share of C programming, so I am familiar with what needs to happen.
First of all you need to understand what C/C++ is. Basically it is a programming language that when compiled properly will execute.

You will need a compiler. I purchased a book and got Borland C++ for free with it. Borland C++ has a compiler that works great. This is helpful because it checks your code for syntax and logical errors. If the compiler doesn't find any errors in your code, then it will convert (compile) it to machine language. That's all automatic, so all you need to worry about is making sense to the compiler.

I recommend you seek a tutorial on basic C programming before you try to take on anything as tackling the code in JA. Below are some online tutorials and instructional sites.
http://www.cyberdiem.com/vin/learn.html)
http://www.accu.org/)
http://knking.com/books/c/)
http://www.jaxnet.com/~garyg/C_ref/C/cref.html)
http://msdn.microsoft.com)

Best of luck.