Seperating Networks

I have an internet cafe which I have recently upgraded to wireless. I have an ADSL router and a W-AP connected directly into the switch portion of it. This first AP is used to supply the shop with ADSL. I have recently purchased a second AP for which I have a largew aerial. I intend to use this to affer other bussinesses in the vicinity accces to the internet using my ADSL router. I have succesfully done this but all the bussinesses have access to my shops network, and can browse the pcs. I’m running XP homw so I cant use domains. can I use subnetting? How? Its class A (10.0.0.x)