I use an Adaptec Gamebridge. You may be able to hunt around and find it cheaper. I picked it up for like $30 on woot a while ago. It's not hi-def and the video is somewhat lacking, but it does what it says it does.
A nifty feature is your computer sees it as a video capture device, like a webcam, so you can stream video from it to programs that use webcams, like chat software.
You might want to try asking for advice in this thread. It's where the numerous 'Let Players' that inhabit the PA forums reside. There should be plenty of people in there who can answer your questions regarding the matter of gameplay capture and capture cards.
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A nifty feature is your computer sees it as a video capture device, like a webcam, so you can stream video from it to programs that use webcams, like chat software.