For openSUSE Factory run the following as root:
zypper addrepo https://download.opensuse.org/repositories/Virtualization:VirtualBox_backports/openSUSE_Factory/Virtualization:VirtualBox_backports.repo
zypper refresh
zypper install virtualbox
For openSUSE 12.2 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/Virtualization:VirtualBox_backports/openSUSE_12.2/Virtualization:VirtualBox_backports.repo
zypper refresh
zypper install virtualbox
For openSUSE 12.1 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/Virtualization:VirtualBox_backports/openSUSE_12.1/Virtualization:VirtualBox_backports.repo
zypper refresh
zypper install virtualbox