Ok I finally found some info on it; notebookreview tested the C7xx series from Compaq, had a 1.4Ghz Core2Duo with 1GB of ram, a 5400 rpm drive, and the same 15.4" LCD, battery life was about 2 hours while watching a movie with wireless enabled.
I don't think they were actively surfing the net while the movie was playing, so I bet if you cut off the movie and started surfing the net, the time would even out to about 2 hours as well.
Might be reason to dump Vista and put on XP.