Ahh, how I wish it wasn't 12° outside so I could use my smoker without freezing my cajones off.
You always want to keep the water tray filled. It helps regulate the temperature and helps keep the meat moist (though the fat in the meat is the primary "moisturizer"). If you keep the temp around 225°-250° and the water filled you ribs will take between 4-6 hours depending on how tender you want them and how much you like to gnaw on the bones vs. the meat completely falling off when you look at it funny (I prefer the latter, but that's just me).
Is that smoker the electric one or charcoal? The electric is more convenient, but you won't get as much flavor as you would with charcoal. I'm a diehard charcoal man so I'm biased, but I see the merit in both. You can add wood chunks to either to get more of the hickory (or apple or pecan or mesquite) flavor.
Here's another site that has a ton of information and recipes:
A lot of the information is about the Weber Smoky Mountain cooker (I have two of them and can't recommend them enough), but the majority can be applied to all smokers.
Just tell yourself that you NEED a smoker to go with your beer habit. It's an easy justification.