The WoW engine was overhauled for the Cataclysm expansion, making use of DX11 capabilities. Whereas WotLK was pretty cushy on systems, Cata is somewhat more demanding.
Unfortunately, there's little you can do in this situation:
Lower your visual settings until you got the FPS you want.
Upgrade your GPU (and CPU I'd say, as they're both a bit dated.)
Buy a new laptop, or even better, a new desktop.
Sorry to herald bad news