Apple - MacBook connecting to wrong network?

If you go to Network Preferences in System Preferences, you should see a button labeled "Advanced" click on that to get to a window with many different network options. Click on Wi-Fi at the top and then rearrange/delete/add networks as you see fit. Then hit ok and you should be good to go! Depending on your OS this may not work, I have no idea. I am on Lion.

I discovered an issue with my home network similar to this. After scratching my head for hours (contrary to popular belief, I have proven this does work!) I discovered one of my four access points was set to WPA2 when all the others were set to WPA security. My devices prefer WPA2 to WPA, and so even when the signal would nominally dictate my devices should be switching AP, they were clinging on for dear life to the weaker signal WPA2 AP. now I have set them all the same and AP roaming works like it should.

If your neighbour's AP is set to 'better' security maybe this is worth looking into. I.e. you have mixed security on your network, your Macs get confused and connect to the unsecured network.... I know, it's a stretch but worth looking at.