I believe that dll is for Studio 2007 to talk to the open source product.
Technically MG Studio 2008 can connect to a 2007 site but various functionalities will not work, joins for example.
The readme for Studio 2008 says this is unsupported.
I would not recommend using Studio 2008 to manage a 2007 Site.
What may I ask is the business case for doing so? If you are just testing 2008 then do so on another machine. Are you not planning on upgrading the 2007 site at some point or is this just for testing purposes?