Sounds like Drop D tuning.
Basically, you tune the bottom E string down to a D.
All it really does though is allow you to get a nice bass sound on a D chord and allow you to do a couple of lead tricks that aren't possible otherwise.
You might be more interested in something like open G tuning which allows you to just barre all the strings to get different chords.

There's a lesson with different tunings on GuitarTricks

http://www.guitartricks.com/lesson.php?input=1754&s_id=7

as well as a tuner with sound files, but you might need full access to get them.