Put on your dimension as a diameter, if you pick the edges SW should add the dia. symbol for you. Then click on properties of the dimension, then the display box, then click the check boxes beside extension line and dimension line. You will have to experiment with first and second to see which makes it work. Those are the SW2007 directions. I just got 2010 and now all you have to do is right click on the extension or dimension line and pick hide.
mncad