If you're talking about Hegemony Gold, the answer is yes! Just go to the game registration page, enter your CD key from Steam, and you're good to go.
If you're talking about Rome, unfortunately the answer is no. Kalypso owns some of the distribution rights to Rome, so we didn't have quite as much flexibility to allow this feature.
Thanks, I have the first games registered here. If rome is ever on sale here sometime then I will re buy it. :)
How about the GamersGate version? can that be registered here?