If I am understanding you correctly, you are trying to access your ABS but your ibook wants to connect to the neighbors wifi. This could be the result of your neighbors wifi having a stronger signal and you have the "join the network with best signal" button on in the network pane of the system preferences (at least that is where it is in os X.2.x
In that same pane, you can always make the ibook use your ABS by clicking "join a specific network."
Are you opposed to locking your ibook to one wifi network because you use multiple wifi networks (work, Borders, etc.)?
I too like the idea of you using WEP. You really don't want anyone to "accidently" using your connection.
Michael