How can I record TV on my MacBook Pro?

I want to record TV on my Mac but I don't know how or what I need. I would like to do it as soon as possible because I'd like to record a television program on my laptop before it expires; I think it expires in 24 hours since it was recorded on my DVR so I still have plenty of time ('til 4 am pacific time I believe). But I'd like to record tv on my MacBook Pro so I can look back and watch what I've recorded.

Unfortunately I do not know what I need for this. If it helps, I have HDTV Plasma's and I record Tv through my Directv DVR but I'd like to record straight to my tv whenever I can't use the dvr. And maybe just record anything that's on my TV for example, video game footage.

Thanks in advance. I'm new to this so please forgive me.