Dubbed Denver B-cycle, the program will require a pair of volunteers at 35 bike-checkout kiosks around Denver for each of the four days. Interested parties should fill out an online application and wait to hear from BikeDenver. Don't call them, they'll call you.
The Denver Bike Sharing deal: $65 a year ($15 less if you're a student), but you can get in on the ground floor for $55 if you register by March 31. This gets you unlimited use of GPS-equipped bikes for 24 hours at a time. But if you hang onto it for 48 hours, your credit card gets billed $750. So don't sign up and then get drunk and get your B-cycle stolen.
Here's a PDF map of the 35 kiosk locations. About 20 of them are in the downtown region, with additional clusters in Capitol Hill, Cherry Creek, and Wash Park/DU. Read up on the volunteering F.A.Q.s here. There's more general info here.