This is repeated (softly) until about :
G-----------------------------------|
D-----------------------------------|
A-----------------------------------|
D--0-0-5-0h3-3h2--0-0-5-0h3-3-2-----|

Here is the fast part! Comes in at :
G---------------------------------------------|
D-2h3h5-----------------2h3h5-----------------|
A------0h2h3-3-x-x-----------0h2h3-3-x-x------|
D-------------------3-0-------------------3-0-|

That is the main riff of the song. There are, however, variations:
At :                              Before the band goes silent:     
G----------------------|	  G-------------------------|
D-3h2h0----------------| 	  D-------------------------|	
A------0h2h3-3-x-x-----|	  A-3-3-x-x-x-3-x-3-x-x-3-3-|
D------------------3-0-|	  D-------------------------|

After the instruments go silent for a bit, you can just
repeat the original riff, only still more softly until 
the fadeout:
G-----------------------------------|
D-----------------------------------|
A-----------------------------------|
D--0-0-5-0h3-3h2--0-0-5-0h3-3-2-----|

*Just as a side note, I'm aware that Colin plays this song a bit
differently live. When Thom starts to sing "I used to think that..."
he begins a tiny improvisation on the D-string:
G-----------------------------------|
D-----------------------------------|
A-----------------------------------|
D-0--12-0-10-0-10-10-12-10-0--------|
You can play it like that with as many variations as you deem
necessary.

That's basically it! A little dexterity, and you've got this song
covered.