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Oh.... Iz Sony vegas Free?
and doesnt a Dazzle come with a editor.
vegas 9 costs like $600(find other ways my boy) now I am not sure if that will run on a mac, which I do not think it does, I do know of software called 'Final Cut Studio' which is just for macs, its quite costly $1000(again, same as above) and just use that to edit.
For someone like me who does not play on an HD TV, I would personally get a easycap as they are relatively cheap(like $15) and can be setup pretty fast and work well. Now if you have an HD tv and actually PLAY with HD quality, then find a capture card that supports HDMI Input.
If you need anything else lemme know, but yeah google, Final Cut Studio, use that, its high end.