Drop D Tuning.
Main Riff:
G|------------------------|
D|------------------------|
A|55-55-5-55-55-0-3-------|
D|------------------------|
2nd Riff.
G|------------------------|
D|------------------------|
A|------------------------|
D|0-8-88-00-5-55-555------|
Main riff again, then 2nd...
Sounds much better with the right overdrive.