Autocad support forum indicates Ver 2006 installs nicely on Win7 except when there is a problem with the installation disc or some other problem that is not Win7 related. Once installed they use WinXP compatibility mode. http://forums.autodesk.com/AutoCAD-2006/
Rt click on the setup file for Autocad and select 'Troubleshoot Compatibility', follow the on-screen instructions. Windows will setup the App in WinXP mode...