Under the Custom selection, at the bottom, there is a minimum optoin in the GUI install.
It is the same as unselecting all the checkboxes (which you can do it Custom on a Text Install)
This will give you what the upstream provider has deemed a minimum install (plus yum added by CentOS for package management).
hmm thats what i did first time around - Text install and unselect everything apart from 'network' and i ended up with X being installed!
Will try the server option and remove everything.