To set up multiple email accounts, you can just use the TOOLS > ACCOUNT SETTINGS menu and configure your 3 different accounts. You will then send and receive email from them all every time you hit SEND/RECEIVE.
If you want to send an email from an account other than the default, you can simply select the appropriate account from the "from" drop-down menu on the compose window.
To seperate your incoming mail, you could set up filters (for example, create a new folder called "Account 1" and then add a rule IF TOfirstname.lastname@example.org THEN MOVE TO FOLDER "Account 1"). I don't use Outlook, so I'm not entirely sure on this, but you might be able to use different inboxes for different accounts - check the help file.
Hope this is some help to you.
I still feel it is not so easy as other email clients do. Microsoft just wants to put so many things together.
Thank you Animal,I think you idea is good
In Outlook Express they were called Profiles. In MS Outlook it takes the Profiles an extra step and lets you configure even more advanced by creating a seperate .pst which is a different user account that is accessed from the same window.
To create a .pst you click on File->New->Outlook Data File (in Outlook 2003) or File->New->pst (in older Outlooks). This will create a new set of Personal Folders in your Mail Folders and for each "Profile" you can create your mail accounts to send and receive however you would like them to work.
Hope this helps.