This is the 6th track on the cd In Absentia.  Great song.
It's easy to play you just have to listen for the bass, it doesn't do the same thing as the guitar does.

riff 1
G-------------|
D-------------|
A-------------|
E-0-1-4-3-6-5-|

the next riff
G----------------|
D----------------|
A------------565-|
E-44-4-565-44----|

the riff after the next
G----------------------------------------|
D----------------------------------------|
A----------------------------------------|
E-4444-765--4444-576--4444-756--4444-444-|

another riff
G-------|
D-------|
A-------|
E-65-43-|

last riff
G---------------------------------------|
D---------------------------------------|
A-----2--------2--------2--------2--5-4-|
E-4444-2-3-4444-2-3-4444-2-3-4444-------|

This is a Porcupine Tree song, not mine so there.