Hylafax / hylamonster how to
Hylafax is a linux server application that can be configured to be the central fax gateway for your business (or home.) Essentially it can deal with queing and sending faxes and receiving them. Faxes can be saved as tiff or pdf files.
The how-to is posted at howtoforge and details the configuration of the server as well as client software. One part of the client software is Cypheus, which is a Windows hylafax client.
More information on Hylafax can be found at their website.