Okay, this is pretty easy... here it goes:

(clean)
-----------------------------------------------
-----------------------------------------------
-----------------------------------------------
---4-4-5-7-5-4---------------------2-2-4-5-4-2-
-5-------------5---4-4-5-7-5-4---2-------------
-----------------5-------------5---------------

-----------------------------------------------
-----------------------------------------------
-----------------------------------------------
-----0-0---0-0-----4-4-5-7-5-4-----------------
-4---------------5-------------5---4-4-5-7-5-4-
---3-----3-----3-----------------5-------------

-----------------------------------------------
-----------------------------------------------
-----------------------------------------------
-----2-2-4-5-5-4-4-0-0-0-0-0-0-0-0-------------
---2-------------------------------------------
-5---------------------------------------------

okay now this part is fast up and down strumming... but still clean

-----------------------------------------------
-----------------------------------------------
-----------------------------------------------
-----------------------------------------------
-16-16-16-16-16-16-14-14-14-14-14-14-16-16-16--
-14-14-14-14-14-14-12-12-12-12-12-12-14-14-14--

-----------------------------------------------
-----------------------------------------------
-----------------------------------------------
-----------------------------------------------
-16-16-16-12-12-12-12-12-12--------------------
-14-14-14-10-10-10-10-10-10--------------------

okay now repeat that four times getting harder and louder as you go.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

this is the loud distortion part before tom starts to sing:

-----------------------------------------------
-----------------------------------------------
-----------------------------------------------
-----------------------------------------------
5-5-5-5-5-5-------------2-2-2-2-2-2------------
------------5-5-5-5-5-5-------------3-3-3-3-3-3

repeat that a couple times
there's your intro... enjoy! :)