I found this article on the web recently which shows how to use the Vista Aero theme on XP in your WPF apps.
I found two things:
01: It is less complicated that the article states.
02: It is a bit different if you already have stuff in your app resources, such as styles or control templates etc.
So here are my steps
01: Add PresentationFramework.Aero to your applications References list. It is listed in the [.NET] tab.
02: Edit your App.xaml and change it from this
<!– Your stuff here –>
<!– Put your stuff here instead –>