Just looking at:http://www.youtube.com/watch?v=qSv9Sdo3VLw
Sounds to me like open D. If you listen to the first upward strum though there is no third, I think he is holding the third string third fret. However if you listen to the 12th fret harmonics you will hear the second and third strings in open D.
From "The Best of Joe Walsh and The James Gang" the opening is open D again, third string third fret hammering on to fret 5.
Sorry can't find any reference to a song "again".