Fax setup with answering machine

I would also like to send and receive faxes on my computer. Is there a  way for the modem to  differentiate between an incoming phone call or fax automatically and either receive the fax on the computer or route the call to the external phone with the answering machine.? I am using Windows XP  Home.
I don't have a separate fax /phone line or number. The phone line is dedicated to my modem for sending/receiving faxes using the built-in XP Fax Server (Fax Console).And I use the same line for  the external phone with the answering machine . I have a broadband connection for internet service . 

If I enable XP Fax Console to "Recieve Fax" , it answers all incoming phone calls(fax or not).I have my answering machine to answer after four rings. Can anyone advice me what is needed to be able to do the above. Thanks for any help. Moe