It depends on the type of hack you want to make. Since you're in the C/C++ forum, I'd suggest you ask your question in the VB/C# forum.
Either way, since you know C# the most you'd be able to do ( without employing advanced techniques ) is make simple trainers for it.
If you want to get `down-n-dirty`and do some more complicated stuff, you'll require knowledge of assembly and experience with reverse engineering.