There are boat loads of customizable features in AutoCAD that affect 3D performance. Unless your friend imported his profile into the new installation of AutoCAD, it is doubtful the settings will be identical between machines.
There are also system variables that can't be found in the menus.
Make sure under Options-->System-->Current 3D graghics display, you are using hardware acceleration with the wopengl8.hdi driver. IIRC the default is software.
Also, though time consuming, this benchmark could be useful, and fun.
If your friend is manipulating files of that size, I assume he is using ADT andknows how to purge a drawing and run an audit. I don't have a file that large, but it takes about 12 seconds to open a 13MB file on my P4 2.6, 1GB, no pagefile, Raptor, old graphics card system. Don't forget the AutoCAD patches.