Hey Lebowski,

These tunes are in DADGAD, which is close to open D, but with a slightly different feel. You might have fun checking it out, for bluesy stuff.
"Swamp Thing" has an especially bluesy sound.
Let me know if these interest you.

DADGAD 1: INTRO, SWAMP THING, SHADY GROVE
http://www.guitartricks.com/tutorial.php?input=502

-Lisa