Welcome! A little patience can go a long way here.
Your processor is very not-so-good. There isn't really anything you can do about that without upgrading the whole platform though. Buying a gtx 550 ti should allow you to play guild wars 2 with acceptable framerates.
If you simply want it playable and need nvidia-based gpus, go with the 550 ti.
If you are willing, the 7770 is more powerful at the same price.
If you want to upgrade the whole platform, you could go for a i3-2120, 2x2gb of ddr3-1333 ram, and the asrock h61m-dgs motherboard, along with a better gpu like the 7770.