You can't expect to play a DX11 game without at least a decent GPU...
Other than that, contrary to what people believe, that PC is enough to play nearly any game on 'medium settings' as long as it's not at high resolution (and you aren't multitasking while playing a game).
There is currently no PC game written for 64bit operating systems. Most are compatible with a 64bit OS but they still run in a 32bit layer. SO, under the limits of a 32bit operating system, it can't even use 3gb of ram nor does it even come close to using the computing power of a quad core processor.
At most resolutions it's the GPU that does the dirty work. Of course, if you're running a powerful GPU in SLI and trying to run a super high resolution on 1, 2 or even 3 monitors that's when other components in your PC would become bottlenecked.