Question : Centos User Interface

I would like a user interface for my Centos. Is there a way for me to run a command that will install it for me?

It is online, but it has no CD drive. I installed Centos originally by putting the hard drive in another computer first.

Answer : Centos User Interface

installing one more desktop environment ( this time Gbnome) will not help as long as X is not configurred properly.
You need to make sure xorg is installed and configurred. Also you have to make your CentOS to boot in runlevel 5 ( full GUI multiuser mode ). I'm assuming you were trying to launch X ( via command etiher startkde or startx ) from withing runlevel 3.
So let's go and install xorg ( video display server) .
then login as root and type : init
which will give you an information what runlevel you're in .
Then ( assuming you have xorg installed already) change to /usr/bin/X11 where X-confuguration tool is located and tyep :  xorgconfig
then follow prompts and instruction so it'd create initial xiorg.conf file.
Once you're done type ( as root) : init 5
in order to switch to runlevel 5.
Type /sbin/service xorg start
Type : startx to launch full graphical user environment ( in your case it'll be KDE)

nedvis