Server 2003 introduces the ability to restore deleted ("tombstoned") objects. This simple command-line utility enumerates the deleted objects in a domain and gives you the option of restoring each one. Source code, which is included, is based on sample code in the Microsoft Platform SDK. This MS KB article describes the use of Adrestore:
840001: How to restore deleted user accounts and their group memberships in Active Directory
Download AdRestore (15 KB)
Download AdRestore Source (32 KB)