Re: What about non-connected computers?
If all you need is XP/7 application support, and not special hardware, then running Windows in a VM is a good solution.
It's a thought, but there are a couple of things preventing that here, I think. First is the hardware. Although it is being replaced as it fails, we still have a good percentage of our machines running 3GHz 32-bit single-core Pentium 4s without virtualisation support in 1GB of RAM. Many of the rest are Core 2 Duos with 2GB, which is better, and the current batch of replacement hardware is AMD A8-based :-)
I've never used a VM in anger, so my second potential problem is that these are machines running interactive software which works best with graphics hardware that can provide a moderate amount of 2D and video decode in hardware. Does that sort of thing work via a VM, or do you just get a framebuffer?
Oh and "special hardware". Yes, come to think of it, we do have a couple of bits, most notable of which are some USB-based hardware key dongles without which the driver for a particular Firewire-attached device won't load.
The installation is 10 years old this year and there has never been a proper replacement plan, nor a migration strategy. In the current financial climate we're just going to have to carry on replacing bits as they fail and hoping we can keep XP alive and safe, but I doubt we'll be the last people on earth using it...