this song is number 4 on the "Purple" album, I haven't seen any really good tabs for 
song's intro so here is one. this doesn't reslly sound good by itself but put it with some 
& drums or play along with the song and you'll see that it's right.

bass plays for about 2 measures and then do a single downstroke on the D chord and rock 
and forth on the wah-wah pedal and hold the chord for 4 beats then start this.

--2-/-5-/-7-/-9----------------------|
--3-/-6-/-8-/-10---------------------|
--2-/-5-/-7-/-9----------------------|
-------------------------------------|
-------------------------------------|
-------------------------------------|

jsut keep the same shape and slide the chord to those spots. pressing down on teh pedal 
each new chord. this is done a few times on the intro and during each chorus.