Get DX11 if you can, if on Windows 8 it should be already DX11, check dxdiag. I'm not sure if integrated graphics is the same but for discrete cards, native DX11 support is needed for some games, meaning installing DX11 does not pass the requirements, the actual card hardware has to support it.
For most MMOs it should be fine with Intel HD 3000 at lower graphic settings. Unfortunately you cant really improve iGPU performance, a discrete GPU will go a long way to improve performance. I would get the latest HD 3000 drivers from Intel and get at least 8GB RAM, try allocating 512MB or more memory to the iGPU in BIOS setting.