If doing up my own campaign, for world Generation, I'd be tempted to look at the old World Builders handbook from DGP. Of course anyone not having a copy, will have "fun" finding one should they want to. The CORPS VDS (Vehicle Design System) claims to be capable of designing vehicles for just about any system. I just picked up a used copy cheap, even though it looks more complicated than I want to deal with.
Personally for starship design, I would like to take a page from the old FASA wargames, specifically Battletech and the Star Trek Starship Tactical Combat Simulator design systems. Have lists, buy a hull from a list, buy a powerplant to put in it from a list, add engines from a list, etc., etc. One guess as to what I played a lot of in the 80's!
Of course as much as I like this system, I'm thinking of going more towards a modular approach (think lego's) for a Sci-Fi game I might do. No real hulls, just clip the various components together. For example, take an engine module, add fuel tanks around it, then a cargo module in front of the engine, followed by a crew module, and finally control module. Each module has its own environmental control systems, each is self contained.
I think someone mentioned writing up starships like you would characters. I believe this is how it is done in the D20 modern system. I also think it makes a lot of sense, just use the same basic combat rules. However, I think that you need a way for crew members to effect how the ship performs. For example, a skilled gunner will increase the likely hood of hitting enemy ships, a skilled pilot will decrease the likely hood you'll get hit. Using such a system needs a way to differentiate between scales. A laser carried by a person might kill another person, but not scratch a starship. A starship laser on the other hand is likely to vaporize a person, and damage another starship.
Zane