copy the directory to a safe place (you can find it in ~/DesktopModules/ )
make a copy of the file that has a name ending in .dnn.config, and strip of the .config
copy all DLL files from the ~/bin dir that are mentioned in the .dnn file you just created. (into the folder where the dnn file is)
most .dnn files require a zipfile, quite often named resources.zip , so create one with a small file in it, (if you want to do it properly, you put all .ascx in that zip)
zip the entire dir (including the .dnn) into some file, and add _00.00.00_Install somewhere in the filename. (preferably the right version numbers instead of 00)
copy the renamed zip into the ~/Install/Module dir.
lets say the module is called "propername"
Now, when you go Host->module definitions (or whatever they are called in your localisation) and you should see your funny filename and version number in the list of uninstalled packages. Click to install the normal way. After that, go to ~/DesktopModules/propername/propername and copy all files there to one directory above that. The files should be in ~/DesktopModules/propername and not in ~/DesktopModules/propername/propername/
I think (but dont know) that if you put all the related files except the .dnn in the resources.zip, then you should not have to move the files up one folder.
I hope someone can confirm this is close to how it should be done.
David.