Here are some pictures of a front-wheel electric assist unit I made for my SWB bent.  It makes hills a breeze!

  It replaces the normal front wheel with a rear wheel from a 20 inch kids bike with a single freewheel cog.  A U-bracket around the forks holds the motor which drives the freewheel through a short chain.  The throttle is a motorcycle style twist grip, and the batteries mount on the bike rack.  The whole thing cost less than $150 to make. The motor and speed controller are from OATLEY ELECTRONICS.

One surprising thing is the the bike feels more stable and the steering is actually improved with the motor running!