With the vertex selected press the shift button and the right mouse button and a menu will pop up. One of the options will be "Split Vertex".
By the way two polygons connected by a single vertex is one of the forms of non-manifold geometry. As such you could also correct this by selecting mesh>mesh cleanup... and then going to the remove geometry section and ensure that "non-manifold geometry" is checked. This should automatically split that vertex.
"If I have seen further it is by standing on the shoulders of giants." Sir Isaac Newton, 1675
Last edited by ctbram; 28-10-2010 at 06:01 PM.