Fixed it, Caren. No sweat.

Shark, of the two options you've mentioned, the 20-long is the better choice for a ball python, although David is right that plastic housing is also a good choice (I have 4 of my BP's in Sterilite enclosures). You will need a hide for each side (warm and cool), and a heat source, for which I also recommend a human heating pad without auto shut-off. Chances are you won't need a humidity-killing heat lamp if you have the heating pad. Your water dish should be heavy enough that it is difficult to tip and big enough for the snake to soak in if it chooses to.

Also, you will need a secure top and if it is made of screen you will either need a room humidifier or you will need to cover most of the screen with something non-permeable such as duct tape or contact paper in order to maintain humidity. I also recommend a digital indoor-outdoor thermometer/hygrometer combination such as can be bought at WalMart for ~$15 to monitor your temps and humidity. The analog (dial type) thermometers and hygrometers like are sold at the pet store are often wrong by a significant amount (sometimes as much as 20F-25F).