I just got a DVD box of RE5 as a birthday gift but have already finished the game multiple times
I can give you the key,interested?
Sorry for the late response pal.
I'll be %100 honest with you :)
The key activates the game in Games for Windows Live (which keeps your save files,allows you to coop etc)
Check this link out:
https://support.steampowered.com/kb_article.php?ref=7480-WUSF-3601#which
According to this page,it won't happen because my posession is a retail DVD box and there is nothing about Steam on it.However you can add the game as a non-steam game to your Steam library.
Personally I have no insistence to play a GFWL game (like GTA IV) on Steam since GFWL provides you all needed features.
If you are not agree with this,I have nothing to say.
:)