My brother has an old old guitjo thing...we found it sounds sooooooo much better with nashville high tuning. It gets rid of that overpowering bass string problem and sounds even more banjo-esque.

Stolen from another site: Essentially, you use the octave strings of a 12-string set on a six-string guitar. The first two strings of your instrument (high E and B) remain unchanged, and the lower four strings (G through low E) are tuned an octave above standard tuning. SIT Strings (www.sitstrings.com) offers a ready-made set for Nashville tuning (P-1025NT), or you can rob a 12-string set or assemble your own from your music store's single-string bin. The gauges for a medium set would be .012, .016, .010, .014, .020, .030, high to low. All strings are plain, except for the low E, which is wound.