Confused yet? Switching from 26t to 24t little ring is cheap and simple. Pair that change with going to the 11-34 megarange and you might likely find that you`ve gotten low enough. I don`t care for those cassettes either because of the big jump on the last shift, but some folks don`t mind. A somewhat expensive alternative to Megarange would be the custom 8 speed 13-34 that Harris offers. Switching to a 22t mtb crankset would give even more granny and could probably be done for about $100 including derailler if you can`t get your current derailler to work with the new rings. If you want to see how much difference any or all of those changes makes (good idea), plug your numbers into an online gear calculator like this one:
http://www.sheldonbrown.com/gears/
One solution that hasn`t been mentioned yet is a Mountain Tamer setup which can give you ungodly low granny for a lot less money than geared BBs or DualDrive. Google them up if you`re interrested.
And for what it`s worth, I can manage about 3MPH on dirt roads, a little less on pavement if I don`t have to pay attention to keeping in a straight line. YMMV.