From what little I know about the Airport, it has two "LAN" connections, an Ethernet one and a USB one.
You should be able to run two PC's at the same time using each of these ports.
There are a couple of potential issues here.....

1. Do you know if the airport is running NAT (Network Address Translation)? In normal situations, DSL modem will run NAT. A quick way to check would be look at the IP address on your MAC (I have no idea how to do this on a MAC). If the address starts with 10.x.x.x or 192.168.x.x then you will be running NAT.

2. Do you run DHCP at the airport (this automatically allocates the IP address to the PC)? Again, your MAC should be able to tell you if the IP address was issues via DHCP.

If the answers to the above are yes, then you should be set to go and be able to run both PC's at the same time (one connected to the Ethernet port, the other to the USB port)

The only other issue you may have may be with you brother inlaws remote access software. If his comapny uses the same private IP adddress range (10.x.x.x and 192.168.x.x) as your router, he may have problems connecting. There is no easy fix to this without changing the IP addressing scheme on the Airport.

Hope this helps!

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