SharePoint - Can I replace a user with another user in sharepoint?

Hi all,
I'm admin of sharepoint. I backup and restore my database in another computer. but my new site does not understand my old user and i can't edit these users. can I replace these users with my new users?
Thanks

At any server, the user name must be import from active directy, first you need to import the all user by using certal adminstion tool shared services.  Then add/replace the users in your current site.

You can use the command  stsadm -o migrateuser -oldlogin DOM\user -newlogin DOM\user