Check out EyeTV for Mac TV products.
Keep in mind, there is no current Mac product that can use CableCard. This means that on most cable tv systems, you won't be able to watch anything other than limited basic (your cable company may have different terminology). Limited basic is typically the local OTA stations, some shopping channels, the weather channel, and local access.
If you have a cable box already, then the EyeTV HD will do the trick, but it needs to be connected to the cable box. But your cable box is probably connected to a TV already, so there's limited usefulness in your situation.
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