Monkey webserver is not available as a package in the Debian repository, you must compile it from source. You can do so with the following commands:

apt-get install build-essential
wget http://monkey-project.com/releases/1.5/monkey-1.5.0.tar.gz
tar zxfv monkey-1.5.0.tar.gz
cd monkey-1.5.0
./configure --prefix=/usr/local
make
make install

Now you can run the server simply with the command:

monkey

You should see the default page if you go to http://your.ip.address:2001

The project has very complete documentation at http://monkey-project.com/documentation/1.5/

FYI: - Monkey HTTP Server v1.5.1 is out - Monkey sources already come with debian/ scripts for build packages (./debian.sh). If you need any assistance with procedures to get this running properly do not hesitate to contact us. Eduardo Monkey Project