I have the same specs (Win7 64 with SharpDevelop), but it works perfect on me.
Here's the path of the assembly of the project (as seen from the solution explorer).
C:\Windows\assembly\GAC_32\DarkGDK\1.2.0.0__e5d518e3875aacb1\DarkGDK.dll
This should be the same on every machine that DarkGDK.NET installer run, correct?
Also there should be these files (thanks to command prompt for copying the filenames

)
DarkGDK.dll
DarkGDK.XML
DGDKLib.dll
DGDKLib.xml
DGDKPlugins.dll
DGDKPlugins.xml
Located in:
C:\Program Files (x86)\Microsoft Visual Studio 9.0\Common7\IDE\PublicAssemblies
If I learn something I will respond.