Clone multiple CentOS VirtualBoxes

Step0:
Enable Virtualization Technology in BIOS  

Step1:
Install CentOS5.7 (Final) with GNOME. This is host machine

Step2:
Install VirtualBox on host machine

Step3:
Create a virtual machine with the following settings:
    System --> Motherboard:
        Chipset: ICH9
        Extended Features: Enable IO APIC, Hardware clock in UTC time
    Storage:
        Controller: SCSI
    Network:
        Attached to: Bridged Adapter

Step4:
Install CentOS5.7 (Final) on virtual machine which is created at Step3

Step5:
Copy file *.vdi to another directory (* = file name)
Execute the following command to change uuid of *.vdi file.
VBoxManage internalcommands sethduuid /path/to/*.vdi

Step6:
Create another virtual machine with copied hard disk.

Step7:
Start new virtual machine

Step8:
Repeat Step5~7 if you want to clone more virtual machine.

How to install GNOME desktop from DVD

Source: http://superuser.com/questions/432000/how-to-install-gnome-desktop-from-dvd-on-centos-6-using-the-command-line

As you have installed CentOS in VirtualBox, and as I understand, while installing you haven't choose X window system, so you are getting black screen with white cursor blinking.

Now what you can do is, install X Window System. If you have internet access in VirtualBox then you can try

yum groupinstall "X Window System"
This will use your internet connection to download the packages and install on system.

If you don't have internet access in VirtualBox then I will suggest you to mount the CD ROM in a virtual machine and install using that.

First of all you need to create a mount point and mount the Installation Media

mkdir /medir/cdr
mount /dev/cdrom /media/cdr
Now you have to create a local repository in /etc/yum.repo.d/

cd /etc/yum.repo.d/
vi local.repo
In this file write

[installation Media]
Name="Centos Local Installation"
baseurl=file:///media/cdr
enabled=1
gpgcheck=0
Now you can install the X Window system using

yum groupinstall "X Window System" "GNOME Desktop Environment"