hockeyref,
Not sure what setup you have or if you have domain vs peer to peer, althogh I think you said peer to peer. Also, are you connecting it directly to your router -- which should be fine. But, basically, you have two ways to go. It does appear that the 9100 is a network printer/fax/scan looking on the HP web site. So, you don't necessarily have to attach it directly to the router, although in effect you will: First, obviously, attach the phone line to your fax line. You can then attach an Ethernet cable to any Ethernet port obviously near your fax line. Now, you can install the fax/print drivers either from a CD or download from HP's site and any computer your install drivers on should be able to "see" the fax machine. The beauty of the networked fax machine is that you don't have to share the machine off another PC thus limiting your faxing or printing to the management of that PC (i.e. if it is off, you can't print/fax and the PC has to manage the spooling). Since it has fax forwarding capabilities, you can digitally receive all faxes instead of via paper giving you the advantages listed above.
Alternatively, if you have a server in a domain environment, you can install the driver one time on the server which will allow all of your PCs to use this print driver to send faxes via the server. This is a slightly better setup, because the server can then manage the faxes for you as far as spooling, etc.
Hope this helps.
