tiltunes

This will let you control iTunes on a Windows machine by tilting your Mac. The following movements are recognized:

on the Mac, tilt to the... on Windows, the effect is...
left back track
right next track
forward play
back pause

Here is a little demo

Here're the programs and the source.

Server (Mac) TiltunesServer.app.zip
Client (Windows) TiltunesClient.exe.zip
Source tiltunes.tar.gz

To run, run the Server on a Mac and the Client on a PC;. When the Client starts up it will print something like My IP is address, like so:

Then to start the Server and enter that address when you are prompted, like so:

The windows app is a zip file because is contains a DLL that has to live next to the executable.