I don't know about multimonitor but if you want to update your catalyst drivers I would suggest that you use the repository method instead of the amd-installer one.
Specifically:
1) remove the ubuntu fglrx which are currently installed:
sudo apt-get autoremove --purge fglrx*
sudo rm /etc/X11/xorg.conf
and reboot.
2) Add the xorg-edgers ppa and install the latest drivers catalyst 13.2 (beta7):
sudo add-apt-repository ppa:xorg-edgers/ppa
sudo apt-get update
sudo apt-get install fglrx
sudo aticonfig --initial
and reboot.
If you are on a true 12.04.2 ubuntu installation and thus running the Quantal kernel and xorg you can leave the ppa in your system and from now on the driver will update it self automatically.
If you are using the precise kernel 3.2.xx you should remove the ppa before the final reboot because it will break your system during the next apt-get upgrade.
To do that simply give the command:
sudo add-apt-repository --remove ppa:xorg-edgers/ppa
sudo apt-get update
you can add the repository back again the next time you'd like to update your drivers.