Yeah, you just got to make sure you start the original Sins (run Sins of a Solar Empire.exe if the launcher doesn't work). The start menu music and the logo at the bottom of the main menu will be different if you did it right. You won't have any of the Entrenchment or Diplomacy features, but you'll be able to play your friend. You'll both have to have the same version of the original Sins though, so make sure you both get the most recent version with impulse.
