The processor or ram is enough to play guildwars, the only problem with MacBook comes from it’s integrated video chip, not really known for his efficiency. But considering GuildWars, it’s now an “old” game which will run without problem on your MacBook, even with your embedded video card.
What graphics card are you running: is it just a simple integrated card or is it a propper card. i.e Nvidia or ATI
you should be pretty good for guildwars though