The main Riff-
for the 5th string down use your middle finger to hold the (7) for the entire riff.
--9-7-6-7--9-7-6-6---|
-7-7-7-7--7-7-7-7-7--|
---------------------|
---------------------|
---------------------|
---------------------|

Background riff/ Riff 2
-----------------------|
-----------------------|
------88-8-44-4-44-4---|
-4-4--88-8-44-4-44-4---|
-4-4--66-6-22-2-22-2---|
-2-2-------------------|

This is the second part of Riff 2 and the end builds up and goes back to Riff 1. Let go 
of palm mute ad build up the end.
Palm Mute = *
-----------------------|
-----------------------|
------88-8-44444444----|
-4-4--88-8-44444444----|
-4-4--66-6-22222222----|
-2-2-------------------|
            ****

Enjoy!