Good evening. Thanks for using JustAnswer. I'm Bruce Mitchell, a/k/a "DrKlahn."
I'm researching HotFax version 6, and it was compatible only with Windows 2000 and XP, so it is safe to say that version 5 won't run under Windows 7.
Smith Micro Software, the producer of Hotfax, has abandoned the product. No newer versions or updates are available to bring it forward into newer versions of Windows -- see their software availability list at the link below:
You could try installing version 6 on your Windows 7 system to see if it works. I've checked the Windows 7 compatibility page at Microsoft, and there is no comment either way on whether it works on Windows 7.
Hotfax version 6 can be downloaded at the following link:
So, in summary: Version 5 won't work. Version 6 might; the only way to find out is to download it and try it.