I am trying to network two computers using a 5 port LINKSYS hub. I am running Scientific Linux on both PC's. It is essentially a souped up version of RedHat. I can go to the Network Configuration wizard and both PC's finds the network cards but gives me a check cable error when I try to activate them. I have checked all the connections and every thing seems fine. The hubs lights are on for both PC's. Can I hook the two computers together simply with one cable going from one to the other? Am I missing some as far as the OS goes? Can somebody help me?

To answer parts of your question: yes, it's possible to connect two computers with one cable (provided both computers have ethernet interfaces, but *all* modern computers have that). However, the cable needs to be a crossover cable (hold the cable in a very oblong U-shape (*not* an O-shape), and look at the plugs at the ends; iff the colored strips of one plug are in the opposite order of the strips on the other plug, it's a crossover cable).

To actually make the computers talk, you need the addressing set up. I'd suggest you give them static private addresses; on my debian box, I'd write the following in /etc/network/interfaces (try grep -r "iface.*lo.*inet loopback.*" /etc/* if red hat places it differently from debian):
(assuming you connect the boxes via eth0). Put the same file on the other host, but with 192.168.1.1 replaced by 192.168.1.2. Now, try pinging 192.168.1.1 from 192.168.1.2 and vice versa. You may also want to find out what /etc/hosts does.

one question. you said you checked all the connections but still get the error right? did you test the cable itself? a bad cable can still let lights work but not transfer info. just a thought.

I have had some problems with 3-com nic´s i stopped using them and now i use realtec (RTL)-8139 card´s without a problem.