Capture cards arent used anymore. The proper term for HD Video recording would be PVR. Happauge HD PVR is the most common used by pro gamers. If you're just experimenting than use a free online capture and see if you like it. But if you're serious then invest some serious money.
Pickup a pirated copy of Dxtory if you're trying to record games and save the video, use FFSplit (It's a free & opensource version of XSplit) to record desktop and stream Dxtory to something like twitch/justin tv