Strange W2K DNS or is it IIS??

Hi,

I have a W2K server running DNS, IIS and Exchange 2K.
The DNS is AD/Private – 123.org. The public DNS is hosted by another ISP that is not local – 123.com.

Sending, receivng mails is fine. But not so when I browse the web pages that is stored in the IIS.
Internal users browsing the web page need to type : 123.org to see the web pages.
While eternal users type www.123.com they got no issue with the web page.
Internal users get an error “The page cannot be displayed” if they typewww.123.com

Is there any way to make it such that the Internal users can type www.123.com and get to access the web pages rather then typing a different URL each time they are in the office or at home.

The same issue with OWA for the Exchagne2K.