Upgrading the OS to 64-bit is so that you can utilize the whole 4GB of RAM since 32-bit Windows does not see more than 3GB or three point something. It may not even be necessary to upgrade just to play Starcraft 2 (though I can't say I'm sure).
Graphic wise, the MSI is probably the best option. According to this website
, you would only be able to play SC2 on low setting, but the MSI laptop is also the only one out of the three that has dedicated card.