Brother has a fax program called PC-fax that prints to the Brother fax printer on the network. I haven't begun using it yet, but it seems to work.
Microsoft has a (rather poor) fax wizard you can turn on in the printers and faxes settings. This should allow you to send a fax directly using your modem and choosing the fax from the printer list. If you share the fax printer you should be able to print from any computer at your office.
I'm not sure if this will help directly, but it may help you find what you need.
