There has been a lot of Mac style Vista themes here and there. But most of are visual styles, which can only give a basic Mac UI to Vista because of the limitations of VS themes. However, when it comes to Wba themes, things tend to be quite different. Look at the following preview picture, can you tell whether it a Vista or a Mac?
To apply this theme, the first thing you should do is to get Windowblinds here: http://stardock.com/products/windowblinds/