OpenSuse does not allow you to install the VirtualBox guest additions ‘out of the box’. You’ll encounter an error message when running the additions binary. Here’s how to solve it…As root execute the following command:
# sudo zypper install gcc make automake autoconf kernel-source
Afterwards you’ll be able to run the addittions binary:
# sudo sh VBoxLinuxAdditions_x68.run
Original information found on: http://jamesselvakumar.wordpress.com/2008/02/23/installing-virtualbox-guest-additions-in-opensuse/