Unless there's a break in the Cat 5 cable, the computers should be able to communicate just like they are now.
Also, the 3Com Lan Modem I suggested would replace the hub you have currently.
My husband bought the hub I have currently...I wasn't sure if it was a good one or not; he is a very good electrician but not much of a computer person at all! I'll definitely take a look at the one you suggest!