Can I play retail games on Steam?

Example: Can I play Steam online with the discs version of Crysis, MW2, Skyrim ect ect?Can I play retail games on Steam?
Skyrim, yes, because it uses Steamworks for its copy protection.



Crysis and MW2, no, because the keys that it comes with don't redeem in Steam. The Crysis key would redeem in Origin (EA's client).



You can always add retail games to Steam as a "non-Steam game" so that it shows up in the list of games, but it doesn't use Steam's servers or download and patching services.Can I play retail games on Steam?
Only if they're available on steam already. I bought a game called World In Conflict a long time ago, before it was available on steam, but it doesn't recognize the cd key i have. But then i bought Border Lands when it was already on steam (because it was cheaper at frys) and i was able to register it and play through steam.

For the games you mentioned, Crysis and MW2 if you bought them recently, then probably. Skyrim you will be able to.