If the install process hangs at:
NetLabel: initializing NetLabel: domain hash size = 128 NetLabel: protocols = UNLABELED CIPSOv4 NetLabel: unlabeled traffic allowed by default NET: Registered protocol family 2
Then you must enable IO APIC for the guest in the settings dialog or append kernel boot parameter nolapic (for installation: linux nolapic | for installed CentOS guest: in grub append to the end of the line begining with kernel nolapic).
Tips for installing using an .iso file: https://forums.virtualbox.org/viewtopic.php?f=7&t=24426
The minimal install file did not seem to find a network driver. Needed to use the full .iso images (this was for a CentOS 6 installation). You can load a virtual CD/DVD iso file by selecting the appropriate pull-down menu option in the Virtual machine. You may need to do this if the system "ejects" the virtual disc. You can also set up virtual CD/DVD drives ahead of time using the virtual machine setup "Settings" menu. Just load multiple .iso images using this process.
Getting the desktop to display full width on the monitor:
First use system-config-display to set the Montor (Virtual Box output) to 1920x1200. Then reboot, then re-install VBOX Guest Additions and reboot once more. Once the machine comes back and you have logged in, you may need to resize/maximize the current window to get the desktop to stretch properly.