I just bought FSX for steam for $US4.99. :D ;D

I don't know how other 3rd party products, like those from Captain Sim, are going to be able to be added or used, YET, but I will find out as soon as I can. ;)

Edit: I have the Captain Sim L-1011 working in FSX for Steam. Not 100% yet. I have to try the following:

Copy the cs1011base.PLN into the Documents\Flight Simulator X - Steam Edition Files folder.
Copy the info from the DLL.XML for FSX to a new DLL.XML file in FSX-SE.

Okay. I did all that, and everything works fine except for the engine effects: cs1011_smoke.fx & cs1011_vaportrail.fx. They are copied to the effects folder in FSX-SE, but I don't see them working. :(