I only play a little banjo, but I can say you should get a banjo that supports using a capo, so it will need the little hooks on the neck for the 5th string that allows you to raise the pitch along with the other four strings that are capo'd.
Also I'd suggest <a href="http://www.musicmoose.org" target="_blank">http://www.musicmoose.org</a> for free video lessons on all bluegrass instruments, including banjo.
Finally, check out <a href="http://www.drbanjo.com" target="_blank">http://www.drbanjo.com</a> and try to get to one of Pete's jam camps or banjo camps. He does a great job.
Hope that helps,
Terry