On my PC, Housebuilder, Layer Manager, and projection_extension show in Preferences>Extensions. I'm not sure about the latest version of SketchyPhysics.
Projection and Layer Manager also have folders in Plugins in addition to HouseBuilder folder. Do you have all their parts in the right places?
Querying the developers for their input might be more useful. Azuby's suggestion too. Flightpathtool and holes, those are RickW's. You could even try contacting him via smustard.com. Didier worked on 3 others. Projection_extension is quite useful. Hope you can get it to work.
A listing might be useful.