Where to find my network password?

I have a small pc network all windows xp, with a Linksys/Cisco router - Wireless-N. When I open up Outlook a box keeps appearing titled: Enter Network Password. It shows server name field, user name field and then a passsword field. Where can I find this computer’s password? Any help will be appreciated.

It’s asking for the username and password of your POP3 mailbox, not something on your local network.