>but if I'm connect with one user , I need say store procedure that he execute the transacs with other different user and password, how can I do.
>Something like "execute as" of sql2005.

You can't do that directly like you showed. Execute is granted to public role. Anyone can execute. However if an SP is not allowed to some role SP doesn't continue.
You should give permission. Check grant, setuser etc. Insetad of username/pwd trusted_connection might be your ticket. You can't grant cross database permissions (and if you have permission to grant you don't need to grant in the first place).
Connect as the user with needed permissions available from the start.
Cetin