What causes a partial blackout?
Check out this post:  http://www.homekb.com/Uwe/Forum.aspx/repair/35373/Service-Entry-Cable-caused-partial-blackout-in-my-house


  Your house is fed with two legs at 120
  volts each.  If you look inside your 
  breaker box, you see three big wires
  coming in, red, black, white.  The red
  and black are legs of 120V, the white
  is the neutral.  Half your circuits 
  are on one leg, half on the other.  A
  220V is on both.   The power company 
  lost one of the legs and so did you.


Looks like what happened to you.