Ok, I've got a Dell Optiplex 740 with a built-in card running Mint 9 (I can't install later versions, but that's another issue!)
I'm running two PCs in my office at working, the aforementioned + a Windows PC. They are attached to the network via a switch, since I only have one ethernet drop available in the office.
The Windows PC works perfectly -- that's how I'm posting this.
The Mint PC was working until I needed to reinstall the system (long story). Now, the Mint PC is connecting to the network. I can even pull up some sites that are local (e.g., owa.med.wayne.edu).
However, the Mint system chokes on other sites, such as this one, cnn.com, etc. I get a connection timed out error from Firefox. The error is not Mint specific -- I also get it in Debian, which I tried -- same issue.