Does Apple's wireless keyboard work cross-platform such as in Ubuntu, Windows and *ixes?
Sure, there's nothing keeping it from working with Windows other than the fact that it's missing some keys. I'm not sure if it's compatible with the various distros of Linux, but you can try it out and look on their associated forums.

Also, for Windows, be sure to check this out:  http://www.kudzuworld.com/blogs/Tech/20080101.EN.aspx