I’ve been lookind for something like this for a while now. I use my PC as my music repository, and I also like to rate my music. The problem I face is that I have to switch over to iTunes every time I want to rate a song. There is no way to do it from the Miniplayer built into iTunes, and I had yet to find a small application (that was free) for Windows that would allow me to do it, like I Love Stars or CoverSutra on the Mac.
Enter SkiniTunes. While not a completly free option, there is a free version available. It currently has two different types of remotes. One is a small one that is just a bit larger than the Miniplayer built into iTunes. The other is a super skinny controller that can easily sit on top of a toolbar. It even has the ability to display a pop-up for the current songs, and allows you to easily rate music while you are listening to it and working on something else. It does utilize .NET 2.0, which from experience has it’s own set of annoyances, but so far so good.
you should also try CD Art Display. Fully Skinnable, and works with a multitude of players.