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EyeTV is probably the only thing available that'll do what you're looking for. They have two versions, one with a coaxial port and another with a composite a/v input.
 
Yup. Eyetv 100% for quality, but certainly not for price. I don't want it for video capture, just for viewing things on my laptop monitor so I don't want to spend £90. If you're wanting video capture, undoubtedly eyetv...
 
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