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Not sure why you'd want to do that, it's a laptop, why not just run iTunes on it and play your media that way.

But to answer your question, It depends on what model your ATV is and weather it's hacked.

The capture card you've linked to only has s-video and composite inputs. The ATV version 1 (old one) has HDMI and component outputs but if you hack it you can connect it via composite so it should work.

However if your ATV is the new one then it only has HDMI out so it's a no.
 
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