I talked to Tiffiney Carney who does all of our trainings. She said the first thing you need to do is set up a 501C3. That's "IRS speak" for a charitable organization. That involves paperwork -- legal paperwork. There's a good summary from the USDA:
http://www.rurdev.usda.gov/rbs/ezec/Toolbox/501c3factsheet.html
There's more information (not as good a summary, but more links) here: http://www.nscsb.org/starting_nonprofit.html
you don't want to get into all that, find an existing nonprofit in your town and partner with it. It's called being a "fiscal sponsor". Basically, you'll send your project's donations through your fiscal sponsor. I found more information on that here:
http://www.ctaconline.org/fiscal.asp
Is there anyone else who has been through this and can offer some other tips?