The good news is that the Elgato EyeTV is exactly what you need and, while it’s classified as hardware, it simply plugs into a free USB port. It also comes with DVR software for Mac that makes it work a lot like a TiVO: you can record shows to your hard drive and then edit them however you want.

http://www.elgato.com/
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I’m a MacHead and a Media Junkie - I have an EyeTV Hybrid and it’s awesome.