The following URL's deal with Faxing over the Internet:
FAQ How can I send a fax from the Internet at http://www.savetz.com/fax/
The Phone Company's Remote Printing Service at http://www-usa.tpc.int/tpc_home.html
Please note that the main issue one encounters when setting up form to fax (as opposed to form to email) is the interface.
Example: Some services will send you a generic CGI script that fits the needs of 90%+ of their clients. However, if they don't fit your need, you will need to know CGI.
Example case where what they give you may not fit your needs:
If you need custom CGI scripts or modifications to existing scripts, please consider utilizing our services.