Edit [2012.12.01] :: The page, and possibly the software itself, no longer exists.  For a free CAD software, you might want to look at DraftSight.

FelixCAD Lite is a fully featured entry level CAD system, with over 300 professional 2D design and drafting functions. Able to directly open drawings saved in industry standard DWG® (upto R.14), DXF® and FLX® file formats, FelixCAD LT is fast and easy to learn with user selectable FelixCAD or AutoCAD® style desktops. FelixCAD LT is free for the first 1 million users who register. They have threatened to withdraw the offer at “any time”, so if you’re at all interested, get it now. There is, naturally, a commercial version with more features.

http://www.givemepower.de/FelixCADlt.html  ~16 Megabytes