Big assumption. I don't know where you live, but I'd be willing to bet it's a neighbor that didn't know how to secure their network, not exactly the same thing.
Not likely to help enough. A directional antenna would probably help if there's some way of connecting one to your laptop. But with built in wireless, I guess that won't fly. Ed Williams has a product that he sells on eBay that might be of interest to you, I think he calls it the Signal Seeker. It wouldn't hurt to ask whoever owns the router how they feel about you tapping into their network.