I have a cable modem plugged into the back of my Apple G4 Dual 125mh Mirror Drive. Lately, I have been getting signals not connected to internet. I found the problem to bee a faulty Ethernet (cat 5?) port that the cable modem wire plugs into. Is this easy to replace or do I have to buy an Ethernet card? If I have to buy a card, can anyone recommend a brand? The video card is AGP.

Should be. An ethernet card is 5-10 bucks. It's no bug deal. I'd go to http://www.macsales.com, they have a tool that brings up all the upgrade for your individual computer. You should check it out.

And how do you KNOW it is the ethernet port on the back on the macintosh? I would not assume a bad port first. I would assume a software issue, defective cable, or defective cable modem(I've had to replace 3 from COX), long before I would think of installing another network card. PowerMac 9600(1 ghz G4) 512mb RAM 50gb SCSI ATi 9200 PCI