there's a Mel Bay Teach Yourself to Play Bluegrass Banjo. You can get it with a DVD lesson for about $20. I used it to learn and found it to be very good and easy to follow. It will not teach you anything about frailin', clawhammer, whatever, but it is a good primer for Scruggs-style. I can also seriously recommend the Deering Goodtime as a starter. I have the resonator model, and it is easy to convert to non-resonator, and very well worth the money. Don't fall for one of the $150 arias or fenders... they sound like a tin-can.
www.banjohangout.org
http://www.ezfolk.com/ (look at the links on the top right of the page)
http://www.unclebens.pwp.blueyonder.co.uk/frames.htmhttp://ourworld.compuserve.com/homepages/Terry_Holland/tutor1.htmhttp://www.paulhawthorne.com/banjo.html(not sure if all of them still work)
Finally, if you don't yet have a banjo, tune your guitar to DGDBGd (Double drop-d with A down to G= open G) This is identical to standard banjo, except the bass D and the G drone is in the bass instead of treble. You can finagle it to practice techniques, so that you practice with a familiar instrument and can hit the ground running when and if you get a banjer. You'll be able to practice both rolls and frails on the guitar, and haved to make only slight adjustments on a banjo.
Five fingers, five strings... Coincidence?