The lisp we use in this course is Franz Inc. Allegro CommonLisp.  It is available at www.franz.com/download.
There are two options here.  

The instructions provided here should be helpful in obtaining and installing ACL:

OPTION 1:    You work on your own computer, and want to download Allegro CommonLisp to run on your particular computer (i.e., at home).

Go to http://www.franz.com/download.  Follow the instructions to download the proper file for your platform.

Choose your platform for your ACL6.2 download.  You can choose Windows or Linux among other platforms.
You will be asked to provide some information, do so, and be sure to enter a valid email address.  You will be sent information on how to continue the download and how to obtain a valid license file.  License files are 60-day licenses, but they may be renewed indefinitely.

Be sure to read the installation instructions.

OPTION 2:     You work on the CS cluster, or you ssh into the cluster.

To setup lisp to run under your home directory on the cluster, simply issue the following command:

~mark/pub/51050/bin/setup.lisp.sh

After running the above script, create or modify your ~/.emacs file, and add the these lines to it.

Then, to run ACL within emacs, simply do this:

cd ~/cspp51050/lisp
emacs -f fi:common-lisp

Now, this will load the lisp virtual machine into an emacs session, which is nice.  For more info on running lisp within emacs, check out the lisp tutorial at /opt/acl/acl62_trial/doc/basic-lisp-techniques.pdf.

Other Lisp resources are on the course home page.