Sorry for late, but I would tell something about that.
I'm not fully sure, but to make programs in C# for WM you can use standard compiler, which is totally free. When i have been making some programs for my WM6 in the past - they were working on the PC platform without any recompiling. But there's one thing to keep in mind - WM uses Compact Framework, that means it's smarter (smaller) version of .NET Framework. However, it should work when you put some simple program from PC into PocketPC.