Song: People of the Sun
Band: Rage Against the Machine
Standard tuning(EADGBe)
This song is a little tricky to get the hang of but once you understand the technique, it's really fun and easy.

For this song, Tom Morello uses an allen key to scrape the strings. However, any metallic object that you have will work the same. For this technique you have to fret A on the 2nd fret and then use the allen key to scrape the string. This will ONLY work if you are scraping in the small area between the bridge and the pickup closest to it. In order to get the sound, all you have to do is scrape back and forth while fretting the 2nd fret on A. For the last note of the riff, simply release the second fret and play open A.

Scrape toward the bridge-
Scrape away from the bridge-/
Let note ring-*

Intro, verse:
E---------------------------- 
B----------------------------
G----------------------------Just play with the scrapes until you get the right 
D----------------------------rhythm.    
A-2-/-2-/-2 0/------------
E----------------------------

Chorus:
E------------------------------------------
B------------------------------------------
G------------------------------------------
D------------------------------------------
A------------------------------------------Let last note ring.
E-23/-23/-23/-23/-23/-23/-23/*- 

This riff is the hardest to play.What you have to do is play the first note normally but for fret 2 on A, you have to slide the object from the beginning of the pickup to the bridge slowly while gradually bending the string.Then, for the last chord, slide the alan key or object across the strings towards the pickguard.
This riff is played occasionally as a variation during the verse. Listen for it and you'll know when to play it.

E------------3----------------
B------------3----------------
G------------x----------------
D------------x----------------
A-0-2^-0/--x----------------
E-----------------------------

That's about it. Figure out when the riffs are played by yourself. It's not hard.