jayandfoo,
to CableForum.
First, do you connect to the Internet through a STB or Cable Modem?
Second, each time you plug in a different device in, you need to unplug the Cable Modem or STB from the mains and plug it back in. Also, shut down the Mac.
Now, plug the Mac in, and plug the Cable Modem/STB into the mains. After all the lights have settled, switch on the Mac. If you have a Cable Modem, you should have an active network connection
If you have an STB, then just start up a web browser and go to
http://start.ntl (I think). You will need your PID and PIN (you'll need to talk to Customer Services if you don't have these).
If you are connecting via Ethernet, you don't need the CD for either the PC or Mac (it won't actually work on the Mac anyway).
Note, the advice I gave above applies if you are switching back to the PC as well.
In the long run, it is easier to get a router, such as the Linksys WRT54G.