This is the #1 thing you need to know. It will drastically affect how you proceed. Note that you don't care what model or brand Mac (ie, hardware) they have; just the version of the MacOS System Software.
Mail them the Mac Diskette package (FreePPP, IE2.1, Eudora) AND MacTCP.
There is one exception to this rule. If (a) they have web access, and (b) they are running 7.5.0 - 7.5.2, then they can download the 7.5.5 Updater, install it on their system, and then use the CD!
Mail them the NetCarrier CD (recommended)
or...
Mail them the Mac Diskette package (FreePPP, IE2.1, Eudora). They should already have a MacTCP or TCP/IP Control Panel (check under Apple->Control Panels to be sure).
or...
If they already (a) have the TCP/IP Control Panel, and (b) have web access, they can get Open Transport/PPP, the "rest of" Open Transport package. Then they can follow the 8.0 setup instructions, below, and ignore FreePPP (however, they still need the Mac Software Package for IE and Eudora).
No software is required! Mail them the NetCarrier CD to facilitate setup. But in a pinch, you can walk them through without the CD.
No software is required! Do NOT send them the CD; you might really screw things up.
Proceed with Chapters 1, 2, and 3 of the 7.X Setup Docs. If you have modem or connectivity problems, check the Links Page for Modem Strings. If FreePPP gives persistently unbearable trouble, it is sometimes easier to settle for MacPPP instead. For this, read Appendix A of the 7.X Setup Docs.
If they have the NetCarrier CD, go straight to the CD Installation Guide
otherwise...
Proceed exactly as "Before 7.5", above, with one major exception. They MAY have the TCP/IP Control Panel rather than the MacTCP Control Panel. IF SO, set up TCP/IP using Open Transport.
If they have the NetCarrier CD, go straight to the CD Installation Guide
otherwise...
8.X+ systems are much easier since they are 100% Open Transport. Ignore MacTCP and FreePPP completely!
If they have the NetCarrier CD, go straight to the CD Installation Guide
otherwise...
These are even easier! Just step through the Internet Setup Assistant and you're done! Or, for slightly more control, you can use the Internet Control Panel.
If problems arise, you CAN go back to the Open Transport control panels themselves. The only difference is that "PPP" has been renamed "Remote Access".
Everything is totally different. Lucky for you, I have screenshots of OS X to walk you through :)
If FreePPP complains that you don't have the right version of MacTCP, consider updating MacTCP. If you get TCP/IP-related problems, consider reinstalling MacTCP.
For modem problems, consider installing a new modem script. Here are some special pointers for Global Village modems.