It is easy to install mISDN and mISDNuser. This can be done by:
You can download latest stable releases from http://www.misdn.org/downloads/
Just fetch the newest head of the GIT (mISDN project moved from CVS) In details this process described here: http://www.misdn.org/index.php/GIT
then compile and install both with:
cd mISDN ; make && make install
(you will need at least your kernel headers to compile mISDN).
cd mISDNuser ; make && make install
Now you can compile chan_misdn, just by making Asterisk:
cd asterisk ; ./configure && make && make install
That's all!
Follow the instructions in the mISDN Package for how to load the Kernel Modules. Also install process described in http://www.misdn.org/index.php/Installing_mISDN