I'd like to add new pre-made dim styles to my file, they are .dwg... How do I do this... import, ex-ref..?????

Help!

I can think of a couple of different ways.  One is to open both drawings and go to the one that has the linetypes you want.  Pick a line that has the linetype that you want, right click and pick "copy with basepoint', pick a basepoint then through the window command open the drawing you want to copy the line type to, right click, pick "past".  You'll be ask for a basepoint, pick a spot there it is....
An easier way is to use Design Center..
 
Then another way is to make sure that the linetype you want is in your template drawing.  That way every time you start a new dwg with a template the linetype is already there.

THis is extremely helpful. Thanks so much for your help.