You install mailadmin into your web directory, by simply un-taring the source package under your webserver DocumentRoot somewhere. My system is Red Hat which by default has a directory path /var/www/html, your path could be different on your system, if you're running another distribution.
cd /var/www/html
tar -xzvf /usr/downloads/mailadmin-1.5.1.tgz
This should give you the directory /var/www/html/mailadmin-1.5.1 with all the code source below that. I found what that I either had to rename this directory to mailadmin, without the version extension, or create a synlink to it. It appears some of the links are hard coded into mailadmin. Depending upon how apache is configured, symlinks may not work.
