Looking for a computer to play Amnesia!

[Your Computer]

and for the comparison, Quadcore's are way better for multitasking and games that require them like the battlefield series, for multitasking you will need a quadcore and some good ram, not a dualcore

Multi-tasking isn't the issue. Nevertheless, when quad-cores first came out they were being outperformed by dual-cores. The reason why should be obvious. Today, quad-cores have more than caught up to dual-cores in terms of performance. As for the topic starter's needs, a dual-core @ 2.8ghz would suite him just fine. As for Amnesia, Penumbra and Skyrim, so would the graphics cards i suggested, all being within the $500 budget.