I suggest you check out Darrell May's how to on ontribs.org.
You will certinaly need an analogue line and modem (external) so you can talk to other fax machines.
I use Hylafax, in receive only mode, on my production ver. 5.5 server which also serves up the internet connection in my small office network. Although fax is "early 20th century", Hylafax is a great way to intergrate fax into a 21st century network. I have all my faxes printed to a printer so my "early 20th century" boss can cope with them (use a postscript printer to save much pain).
It is also possible to have faxes sent as e-mail attachments. Time has prevented me from implementing the next step which is to have faxes emailed to a "fax" account which can be accessed by all via webmail. As the subject line contains the CSID of the sending fax it is then easy to file faxes into folders based on the sending fax CSID....volia all incoming faxes filed automagically! And faxes availible from any machine you make webmail availible to.
Although I do not currently send via Hylafax, options include printing to a fax printer from apps, using clients (WHFC, Cypheus etc) or setting up a email to fax gateway for the less 20th century focused folks.
Anyway IMHO Hylafax is a great way to handle faxes if you still need to and well worth persevering with.
Russ