Contributed By: Cliff Hobbs [MVP ConfigMgr]
Once you've upgraded all of your SMS 2003 Site Servers and Clients to ConfigMgr there are potentially a number of accounts and groups that can be deleted as ConfigMgr no longer uses them.

Accounts
The accounts listed below should be deleted (if they exist), as ConfigMgr 2007 doesn’t use them:

Legacy Client

• Legacy Client Software Installation (defined by SMS Administrator)
• SMS#_dc – CCM Boot Loader (DC)
• SMS&_dc - Client Services (DC)
• SMSCCMBootAcct& – Client Configuration Manager (CCM) Boot Loader (Non-DC)
• SMSClient_<site_code> - Client Connection
• SMSCliSvcAcct& - Client Services (Non-DC)
• SMSCliToknAcct& - Client User Token (DC)
• SMSCliToknLocalAcct& - Client User Token (Non-DC)

Standard Security

• SMS Service account
• SMS_SQL_RX_<site_code> - Site System Database
• SMSServer_<site_code> - Server Connection
  

Groups
The groups listed below should be deleted (if they exist), as ConfigMgr 2007 doesn’t use them:

• SMSInternalCliGrp – Internal client group
• SMS_SiteSystemToSQLConnection_<sitecode> – This group can be deleted after a SMS 2003 Site has been upgraded (until a SMS 2003 Site Server is upgraded this group is still used by Site Servers and Site Systems to connect to their site database servers).