Ignore the post above (sorry mfabien - read up on cable card).
If you have Cable Card, then you will run the coaxial cable into the back of your plasma, and the cable company will activate the card. You will receive all the HD programming, premium channels, and standard channels directly into your TV through the card in stunning detail at the highest possible quality.
The downsides:
1. You will not have the interactive TV guide that is available by using an outboard set top box (STB).
2. You will not be able to get pay-per-view movies like you would with a STB.
3. Cable Card is a VERY new technology and cable companies are being dragged into it kicking and screaming. You may have some problems actually getting it to work. But, I would go for it in a second over my damn STB personally.
I haven't looked at that plasma display.... How are you dealing with audio? Does it have a digital audio/analog audio output? If so, then you really are pretty much set.