i have a ati radeon hd 4870 and i can play guild wars on max with 60 fps steady. But Guild Wars is not a very demanding game and i think you can go with an even cheaper card if that's all you want.
as for Guild Wars vs World of Warcraft.
Guild Wars is great its fun, its easy to get into and its quite deep/lengthy i have 800-900 h invested into it (across 4 years) but World of Warcraft is like a zillion times bigger there's so much to do and see. If it wasnt for the monthly fee i would be playing WoW.
However they are not very much alike, except for the camera view. Guild Wars has 20 levels, which you will reach pretty fast. There is no traditional loot that you collect. Everyone can get the best armor and weapon pretty quickly. (statswise) then if you want some of the more exclusive armors or items you have to put some time into the game, but all they do is look more fancy. Guild Wars is more about PvP, it has a great PvM mode but PvP is where Guild Wars shines.
http://guildwars.com/freetrial/
