I render at high resolution 3d objects but all the curved lines are all sketchy and not smooth.. how is it possible to make these line smooth? PS: Using Autocad 2009Thanks, Dennis

Ok, try this:Type "rpref" and on the top of the window, select the "render preset", select "high" or "presentation". I´m used to save my rendered scenes in PNG format. I hope it works! 

that happened to me. try this, from the "tools" pulldown menu, go to "display", then "display res", then adjust the  "rendered object smoothness". this has impact esp when rendering a rounded 3d object.
 
hope this work.