I would call what Ms. West was doing there, in that excellent rendition of Little Sadie, clawhammer (some would call it frailing or a number of other things) but I didn't see her dropping her thumb to get notes other than on the 5th string. It looks like those fast runs were done with left hand hammer-ons and pull-offs which is similar to the way Doc Watson, and many others approached old time banjo playing. If that is the style you're interested in there is plenty of instructional material out there. David Holt's Clawhammer series with Homespun and Ken Perlman's Book and CD are worth checking out. Also, the Mike Seeger Southern Banjo styles mentioned above is an excellent overview and tutorial of various old time banjo styles and very entertaining as well. When I was starting out I got a lot of stuff from this site which is dedicated to 2 finger thumb lead and has a number of PDF's and Mp3's of old time tunes in various tunings. I don't play that style much (moved on to clawhammer with some drop-thumbing) but I still get tunes off there and jigger them around to what I do. You will also find a lot of info and tabs at Banjo Hangout and some very helpful banjo entusiasts there.