Sharepoint Forum Q & A: MOSS 2007 Mixed Authentication (AD and Anonymous)

Q) Is it possible to create one web application with AD authentication and extend the same web application to another IIS website just with anonymous access?

A) Use Alternate Access Mappings for configuring multiple authenication providers for your site, Each Zone can have its own Authentication settings. For more details check this Article
Plan alternate access mappings (Office SharePoint Server) and Authentication Resource Center for SharePoint Products and Technologies, for Authentication planning & Deployment