Ok. I know on the FAQ page it says that there will never be a Mac port of Messenger Plus, but Patchou is wrong about Mac OS X not supporting APIs. It may not support *his* APIs, but it obviously supports APIs. How else would the OS function?
Anyway, OS X is very simple to use and learn, and it comes with free Developer Tools for Cocoa (Objective-C) and others, like Java and Carbon. Unless there's something I don't know, a port to Mac OS X looks very possible.