i am trying to install openbox on centos.
when i try
yum install openbox
no openbox package available
nothing to do
how can I install this standalone with the yum command?
You will have to find someone who is running a yum repository which includes an openbox package, and include the details in your yum configuration. I've had a brief look, and can't find such a repository, so it seems a little pointless to describe how to add it to your yum config.
However, http://rpm.pbone.net/index.php3/stat/4/idpl/9221302/dir/centos_5/com/openbox-126.96.36.199-5.el5.kb.x86_64.rpm.html has an RPM package for RHEL5 on x86_64 (and therefore for CentOS on x86_64, assuming that you're running CentOS5). Interestingly, it claims the package comes from Karanbir Singh, who is one of the driving forces behind CentOS.
If you're willing to trust an unsigned RPM from the internet (which I might do on a dev system, but never on anything important) you can download the RPM from the link above and install it with
RPMfusion.org now can be installed as a repository on CentOS, and might contain the openbox package (rpmfusion.org)
If that doesn't work, perhaps freshrpms can help, too.
You can try adding EPEL.