For openSUSE 12.3 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/OBS:Server:2.4/openSUSE_12.3/OBS:Server:2.4.repo
zypper refresh
zypper install osc
For openSUSE 12.2 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/OBS:Server:2.4/openSUSE_12.2/OBS:Server:2.4.repo
zypper refresh
zypper install osc
For openSUSE 12.1 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/OBS:Server:2.4/openSUSE_12.1/OBS:Server:2.4.repo
zypper refresh
zypper install osc