If you're running Vista or have .NET on an older OS, you can use the free Galactopedia to explore the techs & the modules and hulls that they enable.

However, your question makes me want to give pushy advice: you'd do best to be designing your own ships, not trying to work through the tech tree in a way that makes any of the built-in ships available. Designing your own ships is fun, and more importantly, developing designs and choosing when to deploy them is a big factor in staying ahead of the AIs.

There's a lot of talk around the forums about ship design, but it basically boils down to one 'universal' guideline and at least one major 'debate' that's driven by play styles and map tastes.

The 'universal' bit is that you're better off doing your own designs because you'll do better if you favor weapon types that the other military powers aren't using and if you make sure you have defenses for the weapon types you are most likely to encounter in combat. The 'debate' bit is about 'the best' hull size(s) to use, and IMO there are too many ways to play GC2 for there to really be 'the best,' with a possible exception for the scoremonster crowd, and even they don't seem entirely united on a particular hull size.