Hi all,
Scan2CAD converts JPG to DXF.
Download the free trial from www.scan2cad.com
It is a fully functional 14 day trial, you can convert pretty much any file to DXF.
They also recently released the article "Pro Tips Convert JPG to DXF " which may help you on your way.
(Disclosure - I work at Scan2CAD, any questions we'd be happy to help.)