This is the main riff. They change it around a little each time, you'll have to listen. 

Intro  
E|--------------------------------------------------|
B|--------------------------------------------------|
G|-----------------------5--------------------------|
D|-----5---5-7---7--5h7-------5---5---7-5-----------|
A|-/7----7------------------7---7----------7-5------|
E|----------------------------------------------8-5-|



When Gregg sings, you strum this:

E|----------|
B|----------|
G|-7-7-7----|
D|-7-7-7----|
A|-5-5-5----|
E|----------|



"But if you leave me" When Gregg sings that you play:

E|---------------------------------|
B|---------------------------------|
G|---------------------------------|
D|---------(b9)(b9)(b9)-7----------------|
A|-5-6-7---7-7-7--5----------------|
E|---------------------------------|