Between Jeff_H and my fellow barn-door-rudder brethren, I don't have much to add. As a relatively new skipper, I can't tell you how much tight marina's scare me. Jeff is bang on with his technical points above... but the original poster is a self-proclaimed newbie which perhaps gives me a more recent perspective since I've recently gone through the same question and discovery.
In my quest for a boat, I sailed on as many as I could. Three examples,
1) I sailed a Shark 24 numerous times ( http://www.shark24.org/membership/images/plan3.jpg
) which was passable but I didn't like the boat. Tacking was easy enough but required a little time to get through the wind.
2) I then had the opportunity to skipper a J24. This thing quickly and accurately pivoted around a central point. It tacked so quickly that I would often over shoot my intended angles. Quick, easy and I needed very little input to get it through the wind in a second.
3) I settled on my lovely little Contessa 26... a modified full keel with a keel hung rudder. Oh boy. If I though the shark was slow through the corners, the full-keel takes a loooong time. I won't be dicing it up in a match racing duel any time with my baby.
From a newbie perspective, the type of keel & rudder combination drastically affects the handling of the vessel. In a car metaphor, a fin keel is going to be more like a twitchy sports car that will respond to lesser steering inputs (to varying degrees of course) and will require greater attention to your course. A full keel will feel more like a limo... you plan your corners ahead of time and will be more forgiving to newbie-skipper steering input. We often lapse in our ability to sail in a steady course for long periods of time. :-)
As a newbie, a full keel seems easier to steer for long distance without the aid of autohelm, but is harder to dock, reverse and handle in tight quarters.
Another point that wasn't mentioned above is the turning radius. From my limited experience, I've found that the narrower the fin keel, the tighter the turning radius. The Farr 30 (Mumm 30) on which I sometimes race spins on a dime as does the J24. The Shark less so but still quite tight. My longer keeled Contessa likes a wide arc. I suspect this is primarily due to keel shape but I'll leave that as a homework exercise for Jeff_H to explain. ;-)