Thanks for replying.
I attempted to install version 2.4 of the API. I have Silverlight version 4 installed.
It is good to know that the .NET references are filtered by Silverlight version.
However, the API dll's are not showing up in the global assembly cache of the machine, regardless of Visual Studio.
I could probably manually add them, but I'd rather not if there's a known reason they're not registering.