Using an alternate outlook 2007 account

Hello,
I have 2 emails addresses one with SBCGlobal.Net and one with Live.com.
Sometimes I have some difficulty to use my SBCGLOBAL email address because of problems inherent to AT&T, I would like to use the my other alternate address which is already set up in my Outlook 2007 account.
Could you tell me how to use it from Outlook 2007. I do not want to write outside of Outlook because I want to use Word in my email.
Thank you very much
Vu