HDPVRCapture enables you to record SD or HD H.264/AAC/AC3 via the Hauppauge HDPVR 1212 on your PPC or Intel Mac.
If you like hardcore, maybe you're hacking your AppleTV and want to record HD on that, then v1.x is a command line only tool exactly for this. Both are available from the Downloads section.
It's simple to install, drag and drop HDPVRCapture into your /Applications folder.