www in web address treated differently in asp.net/flash

I noticed that on our website if users go to myCompany.com (without the www), our asp.net site treats it as a different instanciation of the website or new session. Users are required to login again and our flash applications can't use the web services either. Does anyone know how I can programmatically force a user that types in myCompany.com to redirect to www.myCompany.com?

Thanks in advance.
Matt