[Cube] Airport networks variable

[Dorothy Smith]

My cube and I just moved to the city from the country. I am running  
10.3.9 on a Power Mac G4 Cube. There is an airport card installed:  
Firmware Version 9.52. The neighbors in my new home have given  
permission for us to use their network freely via Airport. At certain  
times of the day two different networks are available, one of them  
strong and fast, the other "linksys" much less so. Can anyone tell me  
how to set up the Cube to always seek the better network? As the  
house is right next door, I can't understand why the variation.  
Thanks for any help, Dotcostume