Thanks! The engine doesn't seem to stumble before it stalls, it just cuts off with no warning. It generally idles just fine, and I don't notice any relationship between stalling and how long the car was cold.
I'm pretty sure the car had a tune-up two years ago (replaced everything). I replaced the battery Fall 2009. I am hesitant to blame the battery because of (a) the ease with which it starts back up again and (b) all of the emergency lights come on briefly when this happens. Its just like when you turn on the battery without starting the engine. The radio only cuts off for a split second when the car stalls.
Is the air intake tube something that I could reasonably check myself(for example, with instructions from you or by googling it)?