Micorsoft IT has implemented several internal IAM solutions and here is a list of links.

Enabling Cross-Forest Identity Management with Microsoft Identity Integration Server 2003:

http://www.microsoft.com/technet/itsolutions/msit/deploy/cfimwiis.mspx

Ensuring Identity Consistency at Microsoft:

http://www.microsoft.com/technet/itsolutions/msit/security/ensidcon.mspx

Structured Active Directory Schema Management at Microsoft:

http://www.microsoft.com/technet/itsolutions/msit/deploy/adschemamgmt.mspx

Group Policy Object Infrastructure Management at Microsoft:

http://www.microsoft.com/technet/itsolutions/msit/security/grppolobjectmgmt.mspx

Managing Active Directory at Microsoft:

http://www.microsoft.com/technet/itsolutions/msit/valuecard/managead.mspx