I'm not sure about free packages.
I bit the bullet and bought a copy of autocad 2000.
2002 and 2003 versions cost loads, but I picked up 2000 with a genuine license for £80.
Still trying to get the hang of 3D, but I was able to do some totally accurate 2D drawings, and the program even draws the measurements on for you. Invaluable when I was giving the plan to the machinist, it wasn't made using CNC, but i think he etched it out on the copper first and then just cut away.
Best bit, if you're making a drill press block, and fancy trying something like a #rotor block, is that you work in real size, so you can draw something up, and print it out as a template.
You just use the program to mark where the centres of the holes are, print it out, stick it to the top of the block, and drill where you've marked.
Something to try anyway