Finally, I was able to try this out. Vista Themes do NOT work in Windows 7. Supposedly because of the new Windows 7 Superbar the theme files are slightly different.
This is a screenshot of Windows 7 and the Vista VBuntu theme. I was able to apply/install the theme but it will only change the wallpaper. The colour theme also changed, but not as expected. Also the taskbar changed but as you can see below it’s the basic grey one.
Windows 7 also introduces “Ease of Access Themes” which only change the colour settings, for example a dark and purple theme (to get a high contrast). Not really useful in my opinion.
Microsoft offers several Windows 7 Themes. Those themes only change the wallpaper, but because of the transparent taskbar the colours change as well.