If you need join existing SharePoint server to your Active Directory domain, then you're in for a treat. Joining the SharePoint server to the domain will mess up the authentication in SharePoint and cause errors. To join SharePoint server to the Active Directory domain without breaking SharePoint authentication:
- Back up all SharePoint content databases and all customizations that you have made to the SharePoint (stylesheets, javascript files, image files, web parts, config files, and so on)
- Uninstall SharePoint completely from the server
- Join the server to the Active Directory domain
- Reinstall SharePoint Server (make sure to use different names for content databases)
- Restore your SharePoint content databases
- Add restored content databases to the SharePoint web application(s) using "stsadm -o addcontentdb" command
- In SharePoint Central Administration >> Application Management >> Content Databases, change status of existing content databases to Offline, and set the status of the recently restored database to Ready
- Copy over the customizations that you have backed up in the beginning (stylesheets, javascript files, image files, config files, and so on) and install missing web parts, features, solutions, etc.
That should be it. Simple, right? J