The Intel HD 4000 is integrated graphics inside the Intel Sandy Bridge generation CPUs. I believe it has 128MB of dedicated RAM and is capable of using up to around 1.5GB of system RAM (normal RAM).
Below is a link to a sample of games that Intel states is "playable". Of course whether or not it delivers the performance you are looking for is a different story.
http://www.intel.com/support/graphics/intelhdgraphics4000_2500/sb/CS-033387.htm?wapkw=intel+hd+4000
I would add Fallout 3 and Mass Effect 3 to the list since I have played those games with the older Intel HD 3000 graphics core. Fallout: New Vegas should be playable, and Mass Effect 1 and 2 should be playable as well.
You need to download a file to play Fallout 3 though. Simply Google for "Odblivion" to find the DLL file that you need to download. Since the DLL file was original developed for Oblivion, that game should also be playable with the HD 4000.