CISCO ISDN Router 770M

I use a Cisco 770M ISDN router to connect my branch office LAN to my head office. The router was configured by the technicians at the head office. I asked them to configure it so that I could connect to the head office server as well as the Internet. But they told me that it was not possible to configure the router in this way. Is it true? Can’t we make multiple configurations in the router so that we can connect to different networks. I do not want to disturb the settings made for my extranet.Please suggest if there is anything that can be done.

Thanx,

Anil