Tutorial 2 has a bug. The output is:
Traceback (most recent call last):
  File "tutorial2.py", line 155, in <module>
    simulate(world, body1, body2)
  File "tutorial2.py", line 141, in simulate
    pygame.draw.circle(srf, (55,0,200), coord(x1,y1), 20, 0)
TypeError: integer argument expected, got float

An easy fix is to replace the "coord" function content with this:
return int(320+170*x), int(400-170*y)
that is, convert to int the values to be returned.

I used the 2010.10.13 snapshot, and I'm running Ubuntu 11.04 32 bits.

Germán Larrain