hi
how can i set the user name and password for opening Enterprise manager?

The username and password of what? SQL Server? A specific account in SQL? Can you be more specific?

-Peter

let me to explain more
my problem is that i have an application that work with database
i don't want any one able to open my database file on the enrerprise manager and modification my data base file manually
help me

I think what you are looking for is simply SQL server security. You need to establish security logins to the database(s) you wish to secure. Provide the appropriate access to whomever needs it. Of course, if someone can access the sql server computer directly (sit down at a terminal or login thru remote desktop) then it's likely that they can just launch the management tools from the terminal with administrative access. I'm not sure what you can do about that.

-Peter

how can i establish logins to my sql database(s)?
how cani provide security for whomever i want?
thanks

Have you tried looking at the documentation?

http://msdn2.microsoft.com/en-us/library/ms130214.aspx

-Peter