This is the CORRECT way to play Immortal.
Tune the lowest string to Dropped C.
Wait for the guitar part to finish, then the bass comes in.
[----------------------------------]
[----------------------------------]
[----------------------------------]  This is played 4 times.
[---0--0-4-4-3-0-2-----------------]

(guitar part again)
[----------------------------------]
[----------------------------------]
[----------------------------------]  This is played 4 times.
[---0--0-4-4-3-0-2-----------------]


This next part is played with the guitar's slow part. This part is played slow. Listen to the song to get the right timing.
[---------------------------------]
[---------------------------------]
[---------------------------------] This is played 4 times.
[----0--4--0--4--0--4--5--4-------]

This next part is the heavy part. 
[---------------------------------]
[---------------------------------]
[---------------------------------] This part is played 8 times
[-0-4-0-4-3-0-3-4-0-4-3-0-4-4-0---]