We are a nonprofit 501(c)(3) corporation. At the 2006 Robotics Conferences at Atlanta another team member and myself presented a session on how to get 501(c)(3) nonprofit status. You can get a copy at our website under the MOE Program/MOE University section at
http://www.fsrobotics.org/moe365//moeu.php
(scroll down to the presentation)
You first become some sort of nonprofit entity, such as a corporation, then you apply for the 501(c)(3) status from the IRS. We did this mainly because we are not associated with a school and having this status allows donors to more easily take a tax deduction. It wasn't hard for us in Delaware but the corporation step is VERY dependent on your state. In the presentation I included links to various state websites, but as this was done in 2006 I can't guarantee that they haven't changed.