Just so people know, you can download C++, C#, VB, ... and some other junk, for free, from Microsoft. It might be an alternative for those people that want to make OP2 levels and don't want to use CodeBlocks. This download comes with an IDE as well as the compiler. Please note that only the C++ pack is particularly relevant to making OP2 levels. Of course some of the others might be fun to download and try out too.
http://www.microsoft.com/express/product/default.aspxBtw, I haven't actually tried to use this version of C++ to make an OP2 level yet. No word yet on how well that works.
Edit: And of course, the MSDN library, in case you need to look up any system related API functions. It's huge and takes a while to install.