>Hi,
>Is it possible to set SQL server to "maintenance mode", which no body can access to database server for particular period using EM or programmatically?
>
>Thank you

Check BOL.

For SQL2K:
In SQL Server 2000, a database cannot be in single-user mode with dbo use only. Instead, the following alternative options are available by using the ALTER DATABASE command:
ALTER DATABASE database SET SINGLE_USER.
This command restricts access to the database to only one user at a time.

ALTER DATABASE database SET RESTRICTED_USER.
This command restricts access to the database to only members of the db_owner, dbcreator, or sysadmin roles.

ALTER DATABASE database SET MULTI_USER.
This command returns access to the database to its normal operating state.

I think there's also a SP to switch modes, check out sp_dboption.