Modem -> Router -> Airport -> Wireless DHCP
Work PC's Static Ip's
It would be a requirement that the wireless connections were on a seperate network that could not see any of the work PC's
Everything depends on the router ..
If the router offers vlan.. then you can set the airport to a different vlan than the Work computers and it will work fine.. But your setup currently is such that wireless clients behind the airport even if they get a different IP address range would still be able to access the work PC's.
Another possible method is to use secondary IP address in the router.. this is same idea as vlan really but some routers offer IP alias.. or secondary IP.. it has a number of names.. This would not fully protect the computers on the main IP address range but via firewall in the computers will effectively do so. It would be important to make sure the local firewall is setup and running.