dwg, dxf how to know reference system

Hello, I am new in this mail list, so please be patient if I do 
something wrong, thanks.

My problem is quite simple(I hope), but still I don't find any solution. 
I have to load in a postGis DB some maps form autocad environment(dwg, 
dxf), to use this dates with geoserver. I have a old version of autocad 
installed in my computer, but I cannot find how to know the reference 
system and projection. Some of you know how to do this, or know simple 
same program which is useful?

Thank you a lot, Antonello Moneta