Or, if you've got BBEdit, type:
bbedit /usr/bin/fax

Find the line that reads:
INIT="-iZ -i&FE0&D2S7=120 -i&C0"

And change it to read:
INIT="-iZ -i&FE0&D2S7=120 -i&C0-SDR=2"

Go to the Print & Fax Panel in System Preferences. Click the Faxing tab. Check the Receive faxes on this computer checkbox.

Set Answer after to 1 or 2 rings. Make sure the # of rings set to answer a fax is LESS THAN the # of rings your answering machine is setup to answer so your answering machine doesn't answer fax calls.

If you don't want to go thru the above;
get a RING SELECTOR device from your local radio shack, set it for #2 - it will filter incoming calls to the fax line
ELSE
get a physically separate fax line. this means never having to hear you phone ring in the middle of the night when a fax call comes in - it's more expensive this way though

I stil have not been able to get the Panther fax sfw. to notify me when a fax has arrived via email.