I would upgrade the graphics card first. If your CPU is a Phenom II, then it is plenty enough to play GW2.
Although you definitely meed the recommended spec requirements:http://www.game-debate.com/games/index.php?g_id=684&game=Guild%20Wars%202
I would wait till it comes out to upgrade. It should be able to play fine, but if you discover you want to play with more of the eye candy on, then upgrade the graphics card.