Draw a line from midpoint?

Is it possible in Solidworks 09 to start drawing a line from its midpoint?  I'm just starting to learn this program (and Mechanical design in general), and a lot of my assignments give dimensions to the centers of lines; it sure would be handy to be able to start a line from its midpoint and not have to constantly figure out the "half-value" of a line.SolidworksSketching