Wanting to switch between E-mail Account

I am using Verizon E-mail. I have 2 accounts there. I created 2 accounts in Outlook 2000 SP3. I want to be able to switch between the two acocunts I have set up. Their web site and techs say this can only be done in Outlook Express. Well, I do not have Outlook Express. I have Outlook! I know this can be done in SP1 or 2.
The acocunts are POP3 Internet mail.
Thanks.