Should I bother buying a dual core processor?

I'm running a really old 2.2 GHz single core AMD processor and looking to upgrade. I'm definitely interested in gaming but really all I'm particularly worried about is running the new Elder Scrolls game (Skyrim) and Diablo 3 when they come out. What I want to know is, should I bother buying a dual-core processor or should I go ahead and get a quad core? Also open to suggestions on what processor I should buy (cheaper the better)