usb cables only put out soo much power. your computer will not charge the camera because it uses too much power. the best thing to do is get an adapter that has a usb in it
if you get one of these it will solve the problem. I have two of them, just plug the usb on the end and it will charge. its also a surge protector so you can rest easy when you leave you macbook plugged in all the time.
http://www.amazon.com/Belkin-Mini-Surge-Protector-Charger/dp/B0015DYMVO/ref=sr_1_5?ie=UTF8&s=electronics&qid=1264906286&sr=8-5