Let me brief u about the project:
iTunes is a music player for MAC but also available for windows platform.
You need to go thru www.ilike.com.
It is a music community site.
They provide a plug-in sidebar for iTunes which you need to download and install in your native machine.
U can refer to the screenshots that I have attached in this mail for further reference.
This sidebar is basically the bridge between the site and user's PC, tracking the songs the user listens to in the native machine and reflecting the information on to the site.
It does a few more things, which we can overlook for the time being.
Anyways, first thing first, u need to build the GUI portion which should get loaded automatically when iTunes is opened in the native machine.
You need to create a dll file and place it inside a folder "\Plug-Ins" which gets created inside iTunes installation folder (when you install sidebar).
Basically, all the plugins for iTunes are placed inside this folder.
There is an SDK provided by the iTunes people, u would get a lot of reference as well as some header files to build your own plugins.