I play clawhammer banjo, too! I'll jump in with a little advice as well.

Either style can be played on either type of banjo (Reed Martin is a fantastic Old-Time player and his banjo on the cover of his album is a resonator; one of the better bluegrass pickers I have met uses an open-back banjo). The difference in type of banjo often has to do with its place in the music. Bluegrass resonator banjos have that metalic, pinging "bright" sound that cuts right through the guitar and bass in a bluegrass band, so those staccatto notes are like marvelous little sparkles all through the melody. But on its own, it tends to be overpowering. Almost painfully so, at times.

Clawhammer (Old-time, Frailing, and a host of other terms that all refer to down-picking) generally suits a voice better and is easier to sing to. If the banjo is likely to be the only instrument played, I think an open-back is better, as it is mellower (not always quieter) and the bump-ditty rhythm (sorry to Dan Levenson, but I do believe in the bump ditty) gives a nice driving backup without the metallic sparkles that work well with a band and poorly with an ensemble. I think clawhammer blends better with a group that doesn't want to sound bluegrassy, but often needs amplification to be heard.

If your friend wants a banjo for playing around a campfire or in the living room, I'm going to suggest an open back. It is friendlier to the ears of neighbors and family who have to endure his learning curve.

A good free resource for learning to play clawhammer banjo is Patrick Costello. He has videos on YouTube under the name dobro33h and his blog is at www.tangiersound.wordpress.com if you want to see what's new with his videos. He makes a living (ostensibly) from his folk-music materials, but makes them available for free as well. Personally, I want a couple of his DVDs that he no longer sells, just because I watched the free online videos from the DVDs and now want the more convenient format I can watch in the bedroom. I will warn you that Costello is not always liked by other banjo teachers. He is sort of an abrasive cuss and people will spend hours in banjo fora talking about how annoying he is. But he's a heck of a good teacher.

Anyway, sorry I don't have a banjo to pass on, but if your friend is handy in the workshop, you might also consider a banjo kit. Then, there's the additional satisfaction of playing an instrument he made himself. I built the kit here: http://www.songsea.com/banjo.htm and my experience with it is detailed here: http://www.angelfire.com/ak5/akboreal/banjossea1.html

-Patrick