Scan the artwork at 600dpi into PhotoPaint. Type Ctrl+B. Set Brightness -25, Contrast +25, Intensity +25. This will remove most of the grain & specks from the image, & isolate black from white while preserving the anti-aliasing (illusion of smoothness where b/w meet). Use the smear brush to remove any remaining specs (undither & blend brushes to remove any "smear trails"... there shouldn't be any though). ImageResample down to 300 dpi & bring the image into Draw. Run your tracing & export to DXF routines now. Should be much, much cleaner...