Setup Network so wireless computers can't see wired ones

Hello all

I have a customer that has a salon/spa that wants to add wireless access for his customers while they wait. He currently has 10 computers on the network. All the computers run his salon software and need to see each other on the network to run the software. Computers 1-9 run win98 and computer 10 has xp and currently is only 1 that has access to the internet. (which is the way he wants it)

Computers 1-9 are connected to a switch
Computer 10 is connected to a router that is connected to cable modem and also connected to switch using the uplink on the router.

How can I add wireless access to the network so that the wireless computers can't join the workgroup that computers 1-10 are on or even know that they are there.

Here is a little picture I put together fast ... might help to show what is going on.

Not sure what this means.
Is the cable modem connected to the WAN port of the the router?

The simplest solution is to place a wireless router between the cable modem and the router you are presently using. Pick a router that does "AP isolation" so that the wireless clients are unable to communicate with each other.