I took DD to the movies when she was about 13 weeks to see Juno (I was watching the movie, not her!) and didn't have a prob, they just said if she gets noisy then I'd have to walk out until she settled, but wasn't ans issue, she just slept through most of it. I did make it a day time so there wasn't many people at all in there.

Also some bigger towns (I saw the movie in SYD) have like a mothers group thing where everyone can bring their children/ babies, so check that out if you're really worried.