Mac os x development to PC

Have you looked at the build settings window yet? There's a little dropdown there, for selecting what platform you want to build for. Unity is quite capable of building .exe Windows executables from MacOS, which will run on any Windows machine.

If you use the web-player, you don't even have to worry about which platform your users are running, because it executes inside a browser plugin (which, unfortunately, still has to be downloaded).