[CentOS] Command Line Commands Aren't Working.....

Ok so I've gone ahead and gotten CentOS to install to a Unetbootin USB, but when I go to install it from there and get the usual command prompt, I try to get a GUI by going "startx"...but I get an error that says "startx: command not found" How do I get the GUI to install from the Live usb? (Mind you I chose the netinstall since it was smaller!) I have tried everything I know...but cannot seem to get the GUI to come up. (This also includes the "yum groupinstall "Desktop environment" command which I’m told is ALSO not found!...what gives?) any advice or help anyone can give would be greatly appreciated!

Cheers!

EGO II