tar xzf rh-isdn-A.BB-C.tgz into a temporary directory and adjust the scripts to your needs before you copy the files to your root-file system. This is for your own safety (refer to the Disclaimer-section). install.sh will copy the files for you and make a needed link!
As you are propably using RedHat you might want to install the RPM, which will hopefully not delete any of the configuration changes you made. I suggest to use the Upgrade-mode of RPM, which will work fine even if you have not installed a previous version of the package. Do this by executing rpm -Uvh rh-isdn-A.BB-C.noarch.rpm and rpm -Uvh rh-isdn-conf-A.BB-C.noarch.rpm for the configuration tool.
Note: Some hints on version: version A.BB-C is the C'th rpm-repackage of the BB'th minor-version of the A'th major-version, so a change in C normally does not provide fixes or enhancements of the scripts but will normally only be a fix of the RPM-packaging.
If you decided to install rh-isdn-conf as well you might skip to do a lot of the changes described hereafter manually. Just execute rh-isdn from the commandline. This will set up the following files: isdn, ifcfg-ippp0 and pap-secrets for you. Make sure to repeat your PAP-UserName in /etc/ppp/ippp0.d/options and to adjust COUNTRYCODE and AREACODE in /etc/isdn/isdn.conf. Then go to Section 6.
/etc/isdn/callerid.conf (some info important for isdnlog)
/etc/sysconfig/isdn (hardware specific settings and choice of dynamic vs. static IP)
/etc/isdn/ippp0.conf (Adjusting hanguptime, country-code etc.)
/etc/ppp/pap-secrets (Username and Password)
/etc/ppp/ippp0.d/options (some other settings)
/etc/sysconfig/network-scripts/ifcfg-ippp0 (ONBOOT and static IP-addresses, Phonenumbers, usage of a slave-device)
Unconnected What you should see if you are not connected
Dynamic IP Changes How route and device-ip will be changed after connection if you have dynamic IP.
On reboot Adding the isdn-script to your run-levels.
Concepts (general)
The scripts (what they do)
1999/12/29, http://www.webideal.de/rh-isdn/