If you want to use more than two virtual machines with the same configuration on VirtualBox, just install one by one. However, this costs lots of time. Instead, I found out how to make a shortcut.
Mothod 1: Use "VBoxManage Clonevdi" command
Method 2: Copy file Win2k3.vdi into Win2k3_clone.vdi and later change UUID.
| VBoxManage internalcommands sethduuid Win2k3_clone.vdi |
The last thing to do is create new virtual machine and the clone disk which is just created.
Have fun!