Changing sender in Outlook

I have 3 email addresses setup as Internet email. When I send an email I want to be able to switch to one of my other email addresses so the receiver sees it coming from bob@hotmail istead of frank@hotmail. What the heck am I missing, this is so simple to do in Outlook Express but I can’t figure it out for Outlook. I’m not logged in as the admin on Y2K Pro either if that has anything to do with it.