I'm not sure I understand the question...
TIF files are compatible with faxinfo and TIF is the default filetype.
eg.
[paul@fax recvq]$ /usr/local/sbin/faxinfo fax000000024.tif
fax000000024.tif:
Sender: 9523801021
Pages: 1
Quality: Normal
Page: North American Letter
Received: 2004:11:17 08:00:41
TimeToRecv: 0:22
SignalRate: 14400 bit/s
DataFormat: 1-D MH
ErrCorrect: No
are you trying to convert a TIF to a PS after it's been created? Try tiff2ps which I believes comes with hylafax.
if you are trying to get the file that is attached to emails be a PS instead of a TIF, change the line in FaxDispatch to read filetype=ps;
HTH,
Paul