Ed Witten, the discoverer of M-theory, is a brilliant man. He realised that 10-dimensional string theory and 11-dimensional supergravity are the same thing. The main problem with M-theory is that not many people can understand it (I sure as hell can't!).
The branes you talk about are areas of a higher-dimensional space called the bulk. For instance, you can have 2 4-dimensional branes (3 spatial dimensions plus 1 temporal) separated by a 4th spatial dimension that is not perceivable from the branes except by the traces that higher-dimensional particles may leave.
There is a theory (called RS1 after its creators Randall and Sundrum) that says there may be what they call a Gravity brane and a Weak brane separated by an infinite, warped 5th dimension. In that theory, there may be higher-dimensional particles called Kaluza-Klein modes. It is possible that the new LHC (Large Hadron Collider) at CERNE may find some trace of some of these particles.