Hi guys,
I was wondering if there is a way to have a mirrored copy of a mesh, let’s say you are modeling a head and want to have a preview of the whole head, so that you can see how the copy half of the mesh gets deformed by moving the verts of the original mesh.
hope this image helps to explain my point.
thanks for your help 
in object mode
alt+d [don’t move it]
then control+m [you probably want the x axis]
with the default settings this would require your object center to be on the plane you want to mirror across, but you can put the cursor there [use shift+s to put it on the grid] and press the period key, then mirror to mirror across a different spot.
Hey z3r0 d, thanks for that bit!
When I made a face recently, I exported into .DXF, and Imported it, that worked, too, but thanks 
Anyway, what exactly does it do?
What Alt+D does? Quote from the manual:
You can create a Linked Duplicate rather than a real duplicate by pressing ALT-D. This will create a new object with all of its data linked to the original object. If you modify one of the linked objects in EditMode, all linked copies are also modified.
You can also just copy something… or simply select multiple objects and then hit ctrl-l this gives you the link menu. Then choose mesh data… it’s also a nice way to link lamps so that they all have the same energy value and you only have to change 1 to change them all.