I may take liberties with the name of the fax program. Since XP has its own fax program and is a descendant of AWFAX or MSFAX, I use that title. If this is unacceptable to you, then I apologise. Just tell me what to call your fax program and we can carry on.
As to Winfax, when such happens I usually have to run it's uninstaller and reinstall it. It's also crucial to know if this is Office 97. Sadly, I've yet to see it work without issue on XP. In fact, a recent escapade was the owner insisting "such and such" worked in 97 on Windows XP. After a lengthy dialogue we discovered it only worked if we installed the older OS, then Office 97. Upgraded to XP and it worked. So far, the feature they wanted has never been seen working without issue if we just install it on XP. Sad that they had to part with money to figure that out.
At this point, my thoughts are still to take Microsoftisms about setting things as this. If it pulls up the fax and the default is something else, then flip the setting to anything else and back to the printer you want.
Your choice,
Bob