If you are in the lucky position of working on a Linux system, installing the required packages can be easily done via your package manager. On Debian-based systems (e.g. Ubuntu) the following command will install everything in one go:
sudo apt-get install python python-pygame python-opengl python-serial python-parallel python-numpy
You can then install Expyriment with the online installer:
wget -P /tmp 'http://expyriment.googlecode.com/files/expyriment_online_install_linux.sh' && sh /tmp/expyriment_online_install_linux.sh
Alternatively, you can download the Expyriment source (.zip) and install as described here.
For Ubuntu, there is furthermore a Expyriment package available through the following third-party PPA: https://launchpad.net/~smathot/+archive/cogscinl)
Switch off desktop effects, when running an experiment
Several window managers nowadays come with a compositing engine to produce 3D desktop effects. To get accurate timing of the visual stimulus presentation it is important to switch off desktop effects in your window manager!