You'll have to pull out the Modem and get Make & Model #'s off of it in order to know what brand it is to find the correct drivers for it. No other way unless you have an old inventory file or documentation of your PC.
I wonder if my '77 Vette had Glasspacks on it? Nah, prolly not, it was a Shovette (Chevette...lol).
Just another stupid saying...