Jets has a good point, for example on how the BSG ships got here:
Cylons were created by the Colonials in the BSG Universe, the Colonials are comprised of 12 planets, or tribes who lost contact with their 13th tribe (earth). Now as we know Freelancer is based on earth growing and colonizing planets in their solar system (Play Starlancer for more info) then war started between the Coalition and alliance which lead to the sleeper ships departing. Who is to say that the battlestar galactica never stumbled on the Sirius system in it's journeys to find earth. :)
