It should be enough to do just:

make
make install

The build was tested on Linux and FreeBSD with 2.x versions of Qt and should
work on others. If you don't have it already, Qt is available at 
Trolltech (www.trolltech.com).

A problem could still occur if your Qt library isn't up to date or if it 
was not correctly installed to compile programs. See the INSTALL file in
Qt for information - your QTDIR environment variable must point to the Qt 
base directory, otherwise you get errors.

Make install will place all files in a common hierarchy below /usr/local/qlwm
(you can change this in the toplevel makefile), one additional link to 
qlwm in /usr/local/bin and a directory ~/.qlwm in your home directory.
The simplest way to make X11 aware of it is however by running qlwm from your
~/.xinitrc file if you start X11 with a startx command or from ~/.xsession if
you use xdm login. You should see something that is preconfigured enough to
start work with it.

See the manpage for information about using qlwm.
The latest version and some additional information can be found at 
http://qlwm.get.to
