Onboard graphics are not in the form of a "card" but rather a chip soldered to the MB. The only wan to know for sure if your onboard graphics chip will handle what you want to do is to try it. You have nothing to lose by doing so and if the performance is not what you desire then add a GPU.
The intel video card built into the i5 is more than enough for everyday computing, and it could easily run the old starcraft broodwar game. That game is locked at 640x480 and 256 colors. It will run on any video device made in the last 10 years. I used to run it back in 1998 on a s3virge 4mb pci card.