I want to create a new user or login, as SQL says, the best way is using the stored procedure sp_addlogin that ships with SQL for this purpose. I tried and really works, created the user or login, but two things happened:
1.- After that, I couldn't logg in using the user and passw that were used with the sp_addlogin.
2.- In the Entrerprise Manager, Security -> Logins, i see the list of SQL users or logins, and on the column Name, the newly created login appears to be larger, although the EM, seems to be correct.

thanks
Felix Martinez