how to define global coordinate system in autocad map 2008

please, how to do this ,,we access that from map ---tool--define global coordinate system,,

for example:if I choose utm coordinate ,,and I have a geotiff image in utm ,,how to do this to get real destance in autocad ,,as arcgis

please ,,and thanks

If the tiff has a world file (.tfw) accompanying it , use Map's Image > Insert

thanks,,but i have a geotiff image in utm coordinate ,,before insert it ,we have to define global coordinate system ,,i have tryed but iam off,, how to do this

Have you verified your units as well?