I managed to get PPP working with Redhat (original Redhat, not RHEL) with the information that Virgin.net provided back in 1997. I did not think that it was too difficult (I also managed to get it working with Breathe without much difficulty). I managed to set Linux up as a router as well, to share the connection with other systems, and even managed to get Internet Connection Sharing working in Windows (95 I think it was).
Neither of them provided specific instructions for Linux, but IIRC it was perfectly possible with the information that they provided for Windows.
I also managed to get Dial-on-Demand working with Smoothwall (a dedicated Linux firewall) a little later, providing protected network access on demand to the proto home network that connected the systems in my home office together. Seamlessly transitioned to ADSL as soon as it was available in my area without having to re-work any of the individual PCs other than the Smoothwall when the change happened.
All those memories...