Yuppers, I surf with mine. When my G4 pooped out a few months back, I used it as my main machine for a month or so; works like a champ. Max out the RAM, pop 8.6 or 9.1 on there, and surf away with WamCom 1.3.1.
I love mine; great machine. Still relatively modern enough to get some things done in today's world, but still old enough to work with all the good old stuff. I'm using mine as a webserver right now
Max out the RAM (128 megs)
G3 upgrade card
USB
FireWire
Anything else your heart desires.
They're basically the same machine, except that the 6500 went to higher speeds. The 6400 had 8 megs soldered to the lobo that the 6500 does not have.