There is a site scifi-meshes.com that might give you some ideas. They had a set of downloads from a lot of the popular movies and tv shows.

You will scrap a lot of models as you find yourself unable to build on what you have aand realize a different method is needed. It happens to everyone.

Realize that especially in Poser you dont need to connect everything nicely. Make a sphere, stick a cylinder into it, add a cone on the end and you have a spaceship sort of thing.  so the sphere, cylinder and cone are not connected, who cares , certainly not poser.