The home page for the SDK (now with new devlopers guide in progress!) is here:
http://www.ciscounitytools.com/CodeSamples/Connection/CUPI/CUPI.htmlon there you'll find a link to the SubVersion repository which is open and available to the public - you just need a free SubVersion client (there's a link to what I consider to be the best and easiest - TortoiseSvn) and you can download/update the library easily - We're updating the library with new capabilities and documentation enhancements etc... a couple times a week at this point. Getting a lot of feature requests and "can you write up how you do X?" type requests going into the dev guide so it's getting a lot of attention.
That's currently the only way we'll distribute the library - there's a little training video out there you can watch that shows how to include and use it in your project if you're not familiar with how to go about that - should get you from A to B on it. It's not scary, I promise - the whole idea of the SDK is to make working with CUPI/CUTI way easier and less painful...