You can use an EyeTV. It's a box that plugs into your MacBook via USB and has a component input on the other end. Run the EyeTV application, choose the AV input and off you go.
Several reviews say there's little to no lag.
Which eyetv product do I need? Link please
EyeTV has a second or two lag. I use EyeTV with a HD-PVR for capturing Gameplay footage on my Mac but it would be unplayable looking at my Mac screen.
The analog input of the EyeTV Hybrid has a delay of only a few milliseconds, allowing for excellent live gameplay.
http://support.elgato.com/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=1063
On other EyeTV devices there's a hardware encoder which slightly delays the display of video, which is why only the Hybrid would work.
So will the eyetv hybrid allow me to play on the MacBook screen?
And I've yet to choose a MacBook air or pro, does that matter?