Watch the Using a Capo online guitar lesson by Ben Wright from Bluegrass Banjo for Guitar Players
Using a capo on the banjo is a little different than on a guitar. On top of the first through the fourth strings, you have to think about the 5th string that's halfway down the neck. There are several options for the 5th string capo, but I prefer the railroad spike. They're cheap and reliable when installed correctly. No matter how you capo, chances are you're going to have to retune a little.