This Steam version of Mass Effect does not have the DRM limits of the EA download version.
As Commander Shepard, you lead an elite squad on a heroic, action-packed adventure throughout the galaxy.
Discover the imminent danger from an ancient threat and battle the traitorous Saren and his deadly army to save civilization. The fate of all life depends on your actions!
*** How to get the "Bring Down the Sky" DLC ***
Once you've installed Mass Effect in Steam, do this...
1. Right click on the Mass Effect entry in your games list, "View Game CD Key" then "Copy to clipboard"
2. Paste the CD key into http://accounts.bioware.com/my_account/mepc_cdkey.html
(signup required first)
3. Look for "Mass Effect: Bring Down the Sky CD Key" on that page and copy it
4. Download and run the installer for the DLC here http://files.bioware.com/masseffect/dlc/MassEffect_BDtS_ES_a.exe
5. When asked for the CD key, you enter the one you copied in step 3.