the Mountain Goats Wiki

Tabbed by Alex Glasnovic (Gray.Fox@gmail.com)

The melody is played by picking the strings in the fashion of D-G-B-E-B-G,
and normally for each chord it's done twice before moving on, except for the 
second E and the chords in the chorus; they're only performed one time through.

INTRO - A D A E A D A E

A                                D
a knocking sound it woke me up,
A                        E
but my legs were feeling weak.
A                              D
i stared up at the ceiling and i saw you at the window.
A                     E        A
but my mouth wouldn't let me speak.

A
i know you.
E                A                    D         A
you're the one i spent three seasons trying to pretend
E            A
that i never knew.

something pulled me off the bed.
and the same thing moved the muscles in my legs.
i moved towards you voice, and my body got so light,
i could've walked on eggs right then and not broken a one of them.

(chorus)x4
//of course, after the first chorus, resort to strumming!//

The Window Song (revised)

Capo 3rd fret:
Verse:
   D          Dsus        D           A           D           Dsus        D     A     D
e----2-----2-----3-----3-----2-----2-----0-----0-----2-----2-----3-----3-----2-----0-----2---
B---3-3---3-3---3-3---3-3---3-3---3-3---2-2---2-2---3-3---3-3---3-3---3-3---3-3---2-2---3-3--
G--2---2-2---2-2---2-2---2-2---2-2---2-2---2-2---2-2---2-2---2-2---2-2---2-2---2-2---2-2---2-
D-0-----0-----0-----0-----0-----0-----2-----2-----0-----0-----0-----0-----0-----2-----0-----0
A--------------------------------------------------------------------------------------------
E--------------------------------------------------------------------------------------------

Chorus:
same picking pattern, chords are D A D Dsus D A D and picked only once, (rather than in the verse where most of them are played twice.)
like this:

       D
i know you.
           A     D                   Dsus      D
you're the one i spent three seasons trying to pretend
     A       D
that i never knew.

There are a few variations in the song, for instance the intro, when he switches from D to Dsus he hits the root note twice and skips the G string, 
or at the part where he says "window" in the first verse, he strums the Dsus a few times.
Play the chorus the 3 last times just strumming the chorus chords, simple enough.