Virtual machine startup

[Tony Yarusso]

We're experimenting here (a college) with the idea of using operating
systems within a virtual machine (either VMware or VirtualBox most
likely) for just about everything, including on desktops, since
different classes use different things.  Essentially what we are after
is a combination of what you would get multi-booting but with easier
recovery/re-imaging, plus the ability for some classes to have
individual installations on removable drives.  Each classroom
workstation should be able to boot from a selection of images on it's
own hard drive plus have the option of using ones on students' USB
drives.  The initial interface needs to be simple, as there are also
some non-computing classes who use these classrooms.  I'm wondering
whether I can accomplish something like the following for this purpose
using Ubuntu:

Have a very minimal actually installed OS
Include the appropriate player (VMware or VirtualBox - willing to
consider KVM if someone can explain it to me and it works for us)
Have the initial screen once the boot is completed basically just be
four big buttons, say three for on-disk OS images, and one for
directly browsing a USB device for one - no login, no desktop
environment, no frills, just basically a secondary "boot menu" in
graphical form, preferably with both names and icons for the
associated OS
Include the ability to drop to a command line / virtual terminal and
use bittorrent to grab new/updated images for the on-disk OS choices,
and easily update the menu buttons to reflect them (can be generated
by directory structure, for instance "display buttons for everything
in /osimages, automatically choosing the size based on total number",
"use /osimages/icons/windows for all images within
/osimages/windows/", "use osimages/icons/linux for all images within
/osimages/linux/", etc.)

Any ideas for what sort of thing could make such an interface?

-- 
Tony Yarusso
http://tonyyarusso.com/