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.

Felix Martinez