Lag only is caused by internet related stuff, not graphical stuff. I.e. when you have a GF4 and a dial up modem 56k and you want to play Everquest and go to a very large andv ery high populated zone, you will get lag. Not becuase your graphic card isn't good, but because your internet connection isn't good enough to download all the files in a proper time.
Graphics don't lag, they drop framerate. So when you have a DSL line but you have for instance a GF2 card, your game will be slow. Why? Not because your DSL line isn't fast enough to download the packets, but because your graphic card, can't handle the calculations it has to make to put everything in the right place on your screen.
Having said that, you should now understand that playing GuildWars won't so much be an issue for all you dial-up modem users, moreover for the ones that are still using a low-end graphic card.
I hope that helps!