Can other computers plug into a macpro to access the internet?

Question

a friend of mine has two macs, a mac pro and a macbook pro.
he wants to access the internet on both computers, (wired DSL)
if he uses his dlink router, the connection is much slower than if he plugs the internet directly into the macpro.
is there a way his macbook pro can plug into the macpro, with its two ethernet jacks, so the portable can access the internet?
we tried it, but it didn't work. Internet sharing was on in the sharing preferences.

Answer 1

At my old workplace I had a G5 with two ethernet cards, a network switch, and a few other computers wired through it. I'm almost positive that I was able to share my connection in the manner that you described. I think that it didn't work right away for me, either, and I had to do some tinkering, but it worked.
Part of the reason why it didn't work was because it was short-lived: our IT department was not happy about having multiple devices connecting through one ethernet jack, and using this method they could see that there were multiple, individual machines on the line (source ID for network requests was different, or some such thing).
My solution - which would also fix your friend's problem - was to turn my G5 into a Squidproxy server. This basically causes your G5 to hand out the IP's to the systems connecting through it, and it forwards on all traffic to and from the computers behind it. As far as I know (based on the fact that the IT department was quiet after I set that up) it'll mask the computers behind it.
Squidproxy is free, but setting it up can be a bit of a chore if you're not familiar with it. It may be an overkill solution, but it'll definitely get the job done.