One thing to note is that NAIP imagery is generally available to the public. Aside from the USDA/NRCS Geospatial Data Gateway, it is also accessible from a number of regional/state-level organizations. A great resource for free orthophotos, NAIP and otherwise, is the World Wind Central section on the topic.
For some practical advice see Jarlath (and particularly the video) on the methodology and benefits of using the Vermont 2008 NAIP imagery in a GIS. 's recent post