Sorry I don't speak German well enough to do this in German.
I downloaded Nehrim, and installed to C:\Games\Nehrim (In the installer it created a copy of my Oblivion), activated the .esm and .esp's, and then moved it to C:\Program Files (x86)\Steam\SteamApps\common and renamed it Oblivion (actual Oblivion I renamed to "1Oblivion"), when I launch it through steam it says "Failed to start game (missing executable)"
How can I fix this?
EDIT: Fixed it, all I had to do was move the entire Nehrim folder into Oblivion (Did this after copying all 9.7 GB's of Oblivion+Mods)