I don't see what the problem is here. You should go out, buy all new hardware in order to support Windows XP (you might want to really beef it up in anticipation of the Longhorn release), purchase a bunch of seats of Windows XP, then go out and buy all new versions of AutoCAD.
What's the problem? If you have 10 stations to upgrade that shouldn't run you much more than about $50,000.00 (US) or so.
Hey, it's the cost of doing business. That should give you a nice warm feeling inside. I know because CADaver told me so.