Of course you can zoom in/out as you draw. I do so all the time. When you are drawing your lines, to zoom, in out, etc just click on the various button, unless of course the tool you are using is the free hand/where ever you move the mouse it makes a line tool (and I never use that tool, except in the most rare of circumstances).

But as Jaerdaph said, best to use paths/polygons in this endeavor.