Outlook 2003 Keeps downloading duplicate emails

I have Windows Office Pro 2003 installed on my home built computer with Vista Ultimate. I have a small business and this computer has been running flawlessly for over 6 months. Yesterday I installed Network Magic from Cisco. Everything worked perfect yesterday including my Outlook 2003. This morning, when I first opened Outlook 2003, everything was good. The, after about an hour, Outlook started to download all my incoming email again..about 1800+ emails! Every time I open Outlook, it wants to download all these emails again. My blackberry (which I receive the same emails, does not do this) nor does the Comcast website, which is my ISP. Why is Outlook 2003 duplicating and downloading all these emails again? Please help.