Will I be able to play StarCraft 2 and/or Diablo 3?

No, not even close, my friend has the Starcraft 2 beta and his computer which is way better than yours couldnt play it. I know you need atleast pixel shader 2.0 and a fair amount of RAM. And looking at diablo 3 graphics which are pretty close to Starcrat 2 I'd say your gona need to upgrade your stuff.