Many people have a hard time installing MS Fax for XP. Here's the fastest way to get all the missing fxs files:
Go to http://www.microsoft.com/downloads/d...displaylang=en
Download the file, but don't run it (it's intended only for Server2003 installations).
Open it with Winzip or other Zip reader.
Save / extract the files to a convenient permanent folder, and point the FAX installation there to access them.