OK, so I have my own Steam account and a boxed edition of HL2: Ep 1 tied to it.
My bro has his own separate Steam account , with his own bought copies of CS:S, HL2 etc. but he doesn't have Episode 1.
Is there any way that my brother can play Episode 1 on his computer? Could he just sign into my Steam account and install Ep 1 from the DVD?
I'm really not sure how this would work.