Thanks for that, but..
I meant without involving VS.NET. That is, editing the .sln and/or .csproj files and/or others.
As an example, I've taken a solution I want to use as a sandbox project -- based on an existing VSS project -- saved it to a non-Working Directory and deleted all the *.*scc files. I then edited the .sln removing the GlobalSection that referred to source control, and I scanned each of the .csproj files involved, looking for any reference to source control -- didn't find any.
When I open the .sln, I still get "This solution appears to be under source control, yet..."
Make it stop! ;-)
Thanks again - Jonathan