The iTunes COM for Windows SDK seems to have been moved from the location they originally had it - http://developer.apple.com/sdk/itunescomsdk.html. It is now inside the Apple Developer Connections site and you need a free membership for it.
Once you have your membership and log into the ADC site, go to Downloads -> Developer Tools. About 1/3 of the way down the page you'll find the iTunes COM for Windows SDK.
(You'll need this if you want to write scripts or programs to automate iTunes from Windows. It used to be really easy to find, but now it's buried, so here's a pointer.)