can't turn key so can't shift gears; pretty sure the battery is dead

To me, it sounds like the steering wheel is locked against its steering lock. This can be if tension is on the steering wheel when the lock engages. To release, simply shake the wheel against it's lock while turning the key. You'll likely find that the key releases. A dead battery will not prevent this. But, a dead battery obviously is a separate concern that will need to be addressed.