Hello myfist0! I'm glad you're interested in modeling, but if I may make a helpful suggestion...if you're just learning how to model with the mod tool you should beginwith some very basic things. I personally use 3ds Max, which has tons of tutorials in addition to numerous video classes and such online. I bet XSI has something similar.
If you already have the hang of that (or when you get it), you should start with a vessel that has plenty of reference pics. It doesn't necessarily have to be "well-known", but you want to be able to see the sides, top, bottom, front, back, and possibly some 3/4 views as well. In the world of learning new skills copying is always one of the first steps, and reference pics are immeasurably helpful with this.
Second, I'm not sure if you're wanting to design ships for the mod, or for your own personal use. If it's for the mod, I'm afraid to say that neither one of those designs will be found withint several thousand lightyears of the "official" product. Stress and other members of the team (admittedly, myself included) take a very dim view of some of the so-called fan designs. While many of them are designed to be awesome in apperance, they just don't have an element of Trek realism that is necessary to fit within this near-canon mod that we're working on.
Third, I suggest you search the internet for some starship design rules. Gene Roddenberry himself created a list of "must-haves" and "cannots" for starship design. For instance, your super cruiser there appears to have 3 nacelles. In the Trek universe, all ships with warp technology must have pairs of nacelles. There are rogue designs that are seen on screen, but they just lack the simple elegance and practicality of the more traditional designs. I see how it might have four nacelles, but that configuration is equally as rare, especially when you get to the larger models like the Sovereign's.
Looking at the battleship, I could go into GREAT detail about what's wrong there, but I'll simply leave it at this: a piecing together of bits of an Akira-class, a full Defiant-class, and a modified Sovereign-class saucer. Uh...no. Just no. My suggestion for you is to go some place like this to see what kind of ship designs exist in canon but aren't seen as game models very often.
Sorry for such a long response, but I and other members of the mod team feel very strongly about this particular issue. If you'd like to practice your modeling and get a better idea of the canon-type designs we could always use another modeler, so I hope you'll keep it in mind. Good luck!