You can do this several ways.
Firstly, you can have one Outlook with two email addresses set up. Outlook
2007 gives you the opportunity to specify separate inbox folders for
different email addresses.
Secondly, you can set up two separate Outlook profiles, one for each email
address. However, you need to close Outlook completely before you can switch
profiles.
And thirdly, you could set up separate Windows User accounts. Each account
would then have an entirely separate Outlook.