What year is it? I know for a fact 97+ use the same key for the door and the ignition. If it's not working in one, then it's not a factory key, and is a bad cut...
Best idea for now? Call a locksmith, have him pop the door open, don't lock it again until you have a new key.
Also, you sure its the battery in the car, and not the one in the remote? If the car won't open you really wouldn't be able to tell...
Edit: Yeah I think your key is a nasty cut, because if you have a remote, no way your car is going to have separate keys for the door and the ignition...
