To do the intro for Even Rats as easy as possible, heres what you should do.
1)Barre the G B and high E strings at the second fret with your index finger, creating a D7 chord
2)Stretch your middle finger to the third fret on the low E string
3) Put your ring finger on the 3rd fret of the B string, creating a D/G chord
4) To hammer-on the 4th fret* on the G string, use your pinky

Guitar 1 (0:02-0:20)
e|-------------2---|-------------2----|-------------2---|--------------2---|
B|---2h4*--------3-|---2h4*--------3--|---2h4*--------3-|---2h4*---------3-|
G|-----------------|------------------|-----------------|------------------|
D|-----------------|------------------|-----------------|------------------|
A|-----------------|------------------|-----------------|-3--------3-------|
E|-3-------3-------|-3-------3--------|-0-------0-------|------------------|

Guitar 2 (0:10-0:20) *position relevant to above ^*
e|-------3--------3--------3---------3--------0--------0---------0--------0-|
B|-------3--------3--------3---------3--------0--------0---------1--------1-|
G|-------0--------0--------0---------0--------0--------0---------0--------0-|
D|-------0--------0--------0---------0--------2--------2---------2--------2-|
A|-------2--------2--------2---------2--------2--------2---------3--------3-|
E|-------3--------3--------3---------3--------0--------0--------------------|

0:21 (Both Guitars)
e|-3-3-3-3-3-3-3---|
B|-3-3-3-3-3-3-3---|
G|-0-0-0-0-0-0-0---|
D|-2-2-2-2-2-2-2---|
A|-3-3-3-3-3-3-3---|
E|-----------------|