You may encounter a few problems when trying to run AutoCAD 2006 on the new Windows Vista.  The following is a quick fix for this problem. 

1) Right click on the AutoCad 2006 desktop icon: 
2) Now click Properties: 

3) Select the Compatibility tab on the AutoCAD 2006 Properties dialog: 
4) Under Privilege Level, check "Run this program as an administrator: 
5) Click Apply: 
6) Now click OK: 



This should allow you to run AutoCAD 2006 on a Windows Vista system.