Thanks Tig and Fiona,
As I suspected the free stuff is pretty scratchy, if it works at all... but I did find Able2Extract
http://www.investintech.com/downloads.htm
Does a good job, converts to DWG as well as DXF, and its possible to set units, line width and scale.
For a $100 it seems reasonable value
Edit:....And thanks Rich and All for the links below