Best thing to do is hold them in your hand. Get a feel for the camera. If you're anything like the rest of us, you'll have 1000 clicks on it before tonight so you want to make sure that you feel comfortable with it.

For that kind of money you can get a killer entry level SLR, D40, D60 or above from Nikon (the Nikon guys will have to give you more info on those - I shoot Canon) or Canon xsi, 40D or 50D. The 40 and 50D are going to eat up all your money. With the xsi you'll get the body and a kit lens and still have $600-700 left over to spend on something else. You don't need much more than that if you're entry level.

This will give you extra money to buy an extra lens (go through B&H or Adorama online to get those, cheaper then Best Buy).