ok, this is a fairly easy method to get to mulgore's secret cave..
FIRST: get on the tb zeppelin(pref from org to tb)
SECOND: you should be looking for a point where the zeppelin crosses between the barrens and mulgore ( about 39, 33 barrens coords)
Imageshack - wowscrnshot110709013650
THIRD: jump off onto this point
FORTH: from there you should be able to find the cave (go downward)
Imageshack - wowscrnshot110709013713
that is all