Additionally, fill Frame Proportionately is a nice new (CS2) option. You can also hold down the Direct Select Tool, as Mr. Levine directed you to, over the picture, count to two, and see a ghosted image of the entire photo... which you can move around inside the frame! You may like to play around with that tool. Really neat stuff, huh. (I'm a newbie too.)

There are actually 5 fitting commands now in CS2. These are on the control pallette but also under Object menu.
If you drag and drop a photo from the Bridge, it does come in full size. Some unrelated tidbits I've recently learned.