Want a Mac look on your Windows machine? Skins and themes would be nice, but there's more to that when you want to REALLY emulate a Mac OSX interface entirely. There are plenty of programs available to emulate specific features of OSX, e.g. Finder, icons, etc [example].

But Flyakite OSX is a project that's looking mature, and it comes with a very complete theme, including sounds and mouse cursors and Explorer customization, things you don't typically expect from a simple 'theme'.

The website goes for a Mac look itself, which is a bit painful, but it's worth the download.

Before you go for it, some caveats

1. The performance of your machine in general may be affected, of course. Not too much though.
2. The theme does fundamentally change some core files like Explorer.exe but (a) it makes a backup so you can go back with a simple uninstall, and (b) it doesn't screw up any additional functionality like my Groove button on my Explorer bar.
3. I don't like shadows under my windows, but that seems to built-in in the skin.
4. Some things like Windows Media Player will not change. WMP has its own skin, which remains untouched.