Can I connect to a specific access point by BSSID?
What OS X version do you have?

In older versions this is possible:


  /System/Library/PrivateFrameworks/Apple80211.framework/Resources/airport -A'NETWORKNAME' BSSID='00:11:22:33:44:55' password='PASSWORD'


But on OS X 10.6 it doesn't work anymore.

I've searched high and low for a solution for this, but haven't found anything yet. The only solution is going closer to your base station. So that the n -signal is stronger.