OK... yes that sounds right.
Now, why you couldn't play the mission:
Because that zip-pack contains no missions. So it tried to load the standard FS campaign. But that ships.tbl only has four ships in it. So it obviously couldn't find all the ships it needed, and so crashed.
Try this: change the name of the D3 ships.tbl file to: d3-shp.tbm. That way, it can still load the main missions and ships while adding the D3 stuff.
However, I doubt you'll be able to play through any missions with the D3 ships unless you alter them so that the D3 ships are under the "Allowed Ships" list in FRED (believe it's under the loadout editor).
As to why they weren't appearing in the techroom... I'm not sure. They should have been, given the way you installed everything...
