I have some music files that are being played, in certain cases in my project. Where should I store those files? I created a folder "Musik" under my project and put it in there, the problem is, how do I get to these files, I don't know the path when it's published.

I don't know the path when it's published

Application.StartupPath returns the path where your application is executed. That path is usually under "Program Files" folder. If you need Vista/Win 7 compatible application, you shouldn't write anything to that folder. Instead, use either Application.CommonAppDataPath (= All Users) or Application.LocalUserAppDataPath (= currently logged in user).