Steam

Release Info
For Steam releases of games, add Valve Corporation as a Distributor, and in the release comments write "Steam release".

Almost all Steam releases should be marked as Worldwide.

Sometimes, Steam displays original release dates rather than the date of release on Steam. Anything before 2005 is definitely wrong. Check the "View update history" or "Read related news" links on the Steam store to see when it was really released on Steam.

Screenshots
First, in Steam, under Settings | In-Game, select "Save an uncompressed copy" and pick a folder to save screenshots to. On this screen you may also set which key to use to take a screenshot (default is F12). Note that this only works for games that are compatible with the Steam overlay, which excludes some older, software-rendered games.