Looks interesting, what little bit I saw.
You'll need the High Def programming package from your digital cable company. You should be able to get OTA HD programming, with the right antenna hooked up. Then you have to have a High Def monitor, to display the High Def content. Otherwise, why bother? Apple's 30" WS Cinema Display, is High Def, and about $2000 or more. Not sure about any of their smaller ones.
I kinda doubt you'll be able to record High Def to the computer. If you can, you'll need a monsterously large hard drive.
Good luck!