If you are using Mdk 8.2, you don't need kppp!
Open Control Centre, Networking, configure internet connection. This configuration wizard should recognise your ISDN hardware and set it up on ippp0 as an ISDN connection. You can then select 64kbs as the default (if you are on the Anytime package it costs you zilch
) and after this has been set up, you can add another profile which uses 128 - obviously using the 128kbs phone number. You get the choice of connection speed during setup.
BTW, don't be alarmed when using the Network Monitoring window, there's a cosmetic bug in 8.2 which shows the text at the bottom as reading 'not connected' when you are connected on an ISDN line - something to do with the card I think.
You can use knetload (on the discs) to put a monitoring applet on the bar, or even use gkrellm if you like twinkly lights
You've climbed the worst hurdle - getting the right Linux compatible ISDN card.
Come back if you need any advice..