Why does the Dealer post the small blind and the other player post the big blind?
Normally the person to the left of the dealer will post the small blind then the second player to the left of the dealer will post the big blind.
So why does this switch when going heads-up?
Quote from Wikipedia
When only two players remain, special 'head-to-head' or 'heads up' rules are enforced and the blinds are posted differently. In this case, the person with the dealer button posts the small blind, while his/her opponent places the big blind. The dealer acts first before the flop. After the flop, the dealer acts last and continues to do so for the remainder of the hand.