you could try reading the "How to's "
on the cent wiki
-- ftp --
I am assuming that this is the current CentOS 6.2
first why did you not install the desktop when you installed cent on this UNNAMED and UNKNOWN host running VirtualBox
pop in the dvd and install the desktop .You can do that with the "upgrade" option on the install dvd
in the terminal ( you have no desktop so everything is the terminal
login as root ( this is fine in the text ONLY mode) and run
yum groupinstall "GNOME Desktop Environment"