Chris,
Set AutoCAD for a HPGL/2 device, the LaserJet III. Doesn't support 600
dpi, but it will give you a 300 dpi plot.
BTW, AutoCAD questions will get their best responses in the AutoCAD forum
(GO ACAD). Since this forum is for the MultiMedia products (like 3D Studio)
this forum doesn't deal with AutoCAD.
Ken ///