(2nd try)

http://sketchup.google.com/download.html

I have not tried it, though I liked the paid for version of sketchup
OK.

Something I have intended to do, but have not got around to, is drawing
machines more or less to "size" (well, a block to size) and their work
areas as flat thin areas they sit on. The idea being that while you
need x feet in front of the mill, that can overlap with or be the same
x feet in front of the lathe (for example.)