Compare:
http://www.startrekreborn.net/images...orbit_1080.jpg with:
http://www.marcblee.org/images/star-...terprise-b.gif.
Whilst it could be said that one may have been heavily inspired by the other (and who could say which way round at this stage?), there are some definite differences - we can only really make out the forward part of the upper saucer from the trailer, but even there you can see some differences that prove that at the very least, Gabe's design as he rendered it is not the ship being used (even if it were his model, it would necessarily have undergone some modifications to arrive at the ship you can see in the trailer).
Trek fans will of course expect the new ship to be pretty faithful to the original - those who understand enough about cinema will also understand the need for the ship to undergo a bit of a transformation to make it look acceptable on the big screen (though it need not be a drastic transformation, even then). But ultimately Star Trek is about the stories; I fully expect a lot of people to pan the film long before they've seen it purely on the grounds that they made the Enterprise look a bit more up-to-date, but I for one am quite content to wait until the thing is actually released and judge it by the story.
Melak: The old conny was the only Starfleet ship seen on screen, though this was almost certainly due to budgetary constraints. I think it was said that there were only 12 of them during the time of TOS, so there were probably other, smaller ships, but we never saw them.