Completely different products. Both do CE type work, but you're comparing
Mechanical Desktop and Inventor.
http://usa.autodesk.com/adsk/servlet/index?siteID=123112&id=3566722
http://usa.autodesk.com/adsk/servlet/index?siteID=123112&id=3096064
On a side note, you should call your reseller. Their job is to explain all
of these things to you and make sure you get the best product for your work.
While C3D can't actually be bought currently, at some point it will be
available.
--
James Wedding, P.E.
IT Manager
Jones & Boyd, Inc.
Dallas, TX
XP/1 on P4-1.6/512
LDT2004+C3D