I am attempting to Install Guest Additions CentOS 64 (guest), Win 8 (host) Oracle's VM Virtual Box quite unsuccessfully. I have tried to follow the method answered here.  But, I get the mount point /media/cdrom does not exist issue also mentioned in the same post.
Install Guest Additions CentOS 64 (guest), Win 8 (host)
centos;virtualbox
A mount point is just a directory, you can create it (as root) with:mkdir /media/cdrom