PS - One cheap and fairly easy way to help you climb hills on that bike is to add a larger rear cog: Harris Cyclery sells and IRD freewheel with 13 - 16 - 20 - 24 - 32 teeth. (Your largest cog right now is probably 28T).

It will require a new chain and rear derailleur though: You can buy excellent 5/6 speed KMC chains for about $5.
For a DR, I would recommend an older long-cage Suntour VxGT, which you can pick up on eBay (or possibly even at the LBS).
You'll have to get a proper claw (hanger) for it from the LBS, Harris, or Loose Screws dot com.