WARNING, untested

Probably you can just install the following package with its dependencies: 
sudo apt-get install openafs-modules-dkms
and then skip to the configuration step below (sudo gedit...). Otherwise follow the following instructions:

Install openafs on ubuntu

Execute the following commands. 
# sudo apt-get build-dep openafs-client
# sudo apt-get install linux-headers-generic openafs-modules-source
# sudo apt-get install build-essential fakeroot module-assistant
# sudo module-assistant prepare openafs-modules
# sudo module-assistant auto-build openafs-modules
The last step described may take a while. If asked give an empty reply to the questions. Go on the following steps, changing the /usr/src/openafs-modules-x.x.x....deb filename with the proper one, which is the one matching your kernel version (use TAB completion!). 
# sudo dpkg -i /usr/src/openafs-modules-x.x.x....deb
# sudo apt-get install openafs-client openafs-krb5 krb5-user krb5-config
# sudo gedit /etc/openafs/ThisCell
Now you've opened /etc/openafs/ThisCell add the following line, if it's not there already: 
cern.ch
Now edit the file /etc/krb5.conf: 
# sudo gedit /etc/krb5.conf
Under the section named [realms] add the following block (if not yet present): 
CERN.CH = {
 default_domain = cern.ch
 kpasswd_server = afskrb5m.cern.ch
 admin_server = afskrb5m.cern.ch
 kdc = afsdb2.cern.ch
 kdc = afsdb3.cern.ch
 kdc = afsdb1.cern.ch

 v4_name_convert = {
    host = {
        rcmd = host
    }
 }
}
And under the section named [domain_realm] add the following line (if not yet present): 
.cern.ch = CERN.CH
Then go on: 
# sudo /etc/init.d/openafs-client start
# gedit ~/.bashrc
In your .bashrc file it can be usefull to add an alias like: 
alias afslog='sudo /etc/init.d/openafs-client restart; klog -principal AFS_USERNAME -cell cern.ch'
You can access the public area of the cern.ch cell even without authentication: in this case you just skip the last step and initialize the openafs-client with 
# sudo /etc/init.d/openafs-client restart