File Sharing while using multiple networks

I am working in a University setting research lab and am attempting to network three Mac computers together.

I have an iMac running 10.6.8, MacBook pro running 10.5.8, and another iMac running 10.5.8

They all connect to the internet via wireless and the University's general connection. I need them to communicate to each other in order to share files. I set up a wired network powered by a linksys router. The computers all connect and obtain IP addresses automatically through DHCP.

I found that in order for the computers to be able to be on both networks and connect the to internet I had to change the "Service Order" so that AirPort has priority.

The problem I am running into is that the computers are only able to connect to each other intermittently. As if the OS is unsure which connection to use for file sharing requests. I frequently get "connection failed" errors when attempting to join another computer, and yet all three computers are always visible to each other.

At one point or another I have managed to get each computer to connect to each other computer, but I can never consistently get all three sharing at once.

Does anybody know if there is a way to instruct the computer which connections to use for specific tasks?

Thank you

Note, you can not be on 2 networks at once. So either you use the University's IP range and extend it, or make a new separate little network with the Macs.

To enable sharing all you need to do is go to System Preferences > Sharing and Enable File Sharing.