I make CAD drawings on a fairly regular basis, and I use a program called DeltaCAD (
http://www.deltacad.com/ ). It is very intuitive and easy to use, almost like MS Paint on steroids. I have used AutoCAD as well, but you almost have to work full time with it to learn and remember how it works. It has so many features that you can't even find the ones you need sometimes. DeltaCAD sure has it's limitations, but it's very easy to pick up and use at any time. It can export and import .dwg and .dxf, so it's compatible with the "big boys" as well.