Layers are the way to go. ideally, differnt parts, line types, colors should be defined by differnt layers: A layer for your 'hidden lines (with the line type set to 'hidden' and 'magenta') one for 'center lines' one for dimensions, etc... Also set the line weights and color. You can set all this up in the layer control dialog box. It's just a good practice / habit to have.

autocad will peridocally require a 'regen' (type 'regen' at the command line) to regenerate the dwg. this should then show the dashed lines & such..

Change the Line scale. Type 'ltscale' at teh command line, and pick a small number. I usually drop down by steps of .25. so, from '1' to '.75' and look at the line types. it'll change all the line scales..

remeber to load the various line types you require....