That's more difficult, because you'd have to make sure that it was compiled for the user's machine. If it is, you can just distribute the .exe (along with whatever dlls etc it needs).
If you only want to distribute the executable, you won't be able to use most of the websites darkestfright mentioned (I don't know about bitbucket, and I'm not sure about CodePlex or Google Code, but SourceForge and GitHub only allow you to host closed-source projects if you pay). You can either get cheap (or free*) web hosting and host your executables on your own website for download, or put them on a file upload website (mediafire is probably the best of these) and just send people the link.
* 000webhost and byethost (byet, not byte, I don't know why) are the only ones I know of, but I'm sure there are more. The only problem here is that you won't be able to store massive amounts of data, probably only a few hundred MB or even 1 GB (easily enough to store several reasonably sized projects, especially without the source code, but nowhere near enough for the average modern commercial video game).
You only need to recompile it with a compiler for Windows, you don't need to change the code unless you were using Mac-specific functions. There seems to be a MinGW port for Mac, so if you can get it to work, you can compile for Windows directly on a Mac.