Does anyone know how to write a SQL Server stored procedure that will check if an item is in a database? Here is what I have at the moment, but it doesn't seem to be working:

CREATE Procedure sp_mdLoginUser
@Username varChar(50),
@PassToken varChar(50)
As
DECLARE @UserID int
SELECT
Username,
PassToken
FROM
Users
WHERE
Username = @Username
If @@error = 0
BEGIN
SELECT @UserID = @@IDENTITY
return @UserID
END
ELSE
BEGIN
return(0)
END

Thanks