Thanks a lot. I compiled the Mono Addin, restarted my SharpDevelop, and created a new application choosing the Mono "Gtk# Application" option. That compiled and ran, and then I set the run up to use Mono. All this according to the link you sent.
I just need a bit of clarification at this point. When I go to the Properties page for the project, I still see that Target Framework under the Compiling tab doesn't show Mono as a target. (A previous page I had seen said that I should see Mono as options here and choose it that way, so I'm wanting to understand this choice.) The Target Framework option has 5 options, all of them version of the .NET Framework. I am assuming that I could choose any one of these and it would change the version of the framework that Mono is using for the build, as long as I had that framework version installed. Correct?
Thanks again...