Well, this tiddy has eluded me... because chordwise there's nothing happening.
I think it's:
Dm ... for forever... then drops down two frets to C for the instrumental break part. At least live versions appear to be like that.
The bass line drives the songs. Sometimes live it's been just D A D A bassline, but other times with a A C walk-up back to D.
Looks like it was played two frets down here in 2004: http://www.youtube.com/watch?v=CZZvgj1iLCE