If I'm replicating a server with 4 instances on this
server. What's the best way to move the users with it,

How are you moving the database? If you are using backup/restore, then the
database will retain all the users, but you need to make sure there are
matching logins in the master database of the target server. Otherwise,
these users will be orphaned. You could use sp_change_users_login to
associate users with their corresponding logins. For more information see:
http://vyaskn.tripod.com/troubleshooting_orphan_users.htm

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HTH,
Vyas, MVP (SQL Server)
http://vyaskn.tripod.com/
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[quoted text, click to view]
If I'm replicating a server with 4 instances on this
server. What's the best way to move the users with it,
without deleting and recreating them?