I'd just like to clear up any confusion arising from the use of the term 'six-string banjo' in a couple of the above posts. The six-string banjo is not the same instrument as the guitar banjo. It has five long stings plus the octave string. It's like a five-string with the addition of a low G. The seven-sting banjo has the low G, with a C string between this and the D. These banjos are not just for people who "can't be arsed learning to play a proper banjo". One might just as well claim that the fretted banjo is for people who "can't be arsed learning to play a proper banjo".
Light blue touch paper and leg it... John Kelly.