Too Cold?

Since I'm a cheap student who's trying to save a bunch of money, I'm living in the top floor of a house owned by an elderly woman (the rent is very low, i.e <$500)

It has a living room, bathroom, and bedroom. The only room that has decent heat is the bedroom. I live in western MD and during the winter it drops below 20 degrees frequently.

Now, it probably won't get that cold up here, but it'll still get nippy. Will that hurt my MacBook? I keep it running all the time.

Thanks.

From the Electrical and environmental requirements section of the MBP tech specs page:
Operating temperature: 50° to 95° F (10° to 35° C)
Storage temperature: -13° to 113° F (-24° to 45° C)
Your Mac will be happier at a lower temp than higher! The only caveat is rapid temperature change, that can cause condensation and stress cracks.

It will be fine. Unless you leave it sitting in the cold and then bring it in where it's warm, where as Sherman mentioned, you may cause condensation. I don't think stress cracks will be an issue, generally those only happen if the temperature change is very rapid (as Sherman also mentioned) and very large. Walking from a 65*F room to a 70*F room is a rapid change, but it's not gonna hurt anything. Sticking your mac in the freezer and then dumping it under a heat lamp might cause stress fractures in the plastic, but barring that, it shouldn't happen.

Well, even though those specs are for a MBP, I'll probably be fine.

I wasn't sure if LCD screens could be damaged by low temps, so i was just wondering.