If you read the sticky from the beginning, you will see that Boot Camp is preferable if you need full acces to your graphics hardware. You didn't tell us what kind of Mac you are using but if it has a separate video adapter you will likely see a performance improvement for AutoCad in Boot Camp. You'll have to reinstall windows for this to work.

Virtual machines use a "virtual" graphics adapter (software) which is fine for productivity applications, surfing, watching DVDs, etc., but for heavy video editing or rendering packages, you will see performance issues under any virtual machine.

Hope this helps.

Cheers