No telling how many monitors your system can support. It may be that you can use both the HDMI and VGA outputs, but it's just as possible that your system can only use one of the external outputs at a time.
That being said, you could use something like the Matrox TripleHead2Go to expand the number of external monitors you connect, but this is only something you'd want to use for productivity, not gaming.
-Wolf sends