I installed FO3 through Steam today to my PC but I can't seem to find where it was installed, so I cannot find out where to place my mods. Any help please?

look here---------- C:\Program Files\Steam\SteamApps\common

thats where my steam games are

hope that helps

Indeed it did, my friend.
Thank you very much.

If you have Vista or 7 and are using the Program Files folder, UAC may cause trouble with mods. I have Steam in C:\Games\ for that reason.

just in the event you did not know, your better off using http://www.fallout3nexus.com/downloads/file.php?id=640

instead of dumping the mods in there

must have imo