if you managed to mine on the video card you could pull an amazing 6 megahashes/sek or something....which means you would only waste electricity because you need about 100 macbooks to generate the power of one 5970 which costs 600 bucks.
I have an old desktop with 4 gigs of ddr2 and an nvidia geforce 9600 GT, would it be worth it then?
nope. you would still waste more money on energy - nvidia cardes are ineffective for mining, buy ati and win.