I believe Autocad 2008 is compatible with vista. You can also check the same from http://www.microsoft.com/windows/compatibility/Details.aspx?type=Software&p=Autocad%202008&v=Autodesk&uid=&pf=0&pi=0&s=autocad%202008&os=32-bit
However you may like to take a look at the links below,
Hope the above helps.
NOTE - Disclaimer
The links in this message may lead to third-party Web sites. Microsoft provides third-party resources to help you find customer service and/or technical support resources. Information at these sites may change without notice. Microsoft is not responsible for the content at any third-party Web sites and does not guarantee the accuracy of third-party information.