just back click, make sure you are on vertices and then just click on the vertex. if it's selecting that vertex and another on the opposite side, then you possibly duplicated with instance selected so that you could work on both sides of the model at the same time - just delete the other side.
if its not that, post a pic so we can see what you mean.
Last edited by arran; 20-11-2008 at 06:50 PM.