I'd like to create a grid of PCs on which to run virtual instances of WinXP. What is the best method? I have a number of dual-core intel desktops and I'd like to run a few of them to create a high availability environment on which to run one or more instances of Windows XP.
Honestly this sounds like a poor way to start. If your computers only have 32 bit processors, I'd just stop right there, you'll never get very good performance out of it, and it'll almost certainly be more trouble than it's worth.
You'll need some form of shared storage. A FreeNAS box can provide iSCSI storage that most virtualization packages will happily use. I'd go with Hyper-V or ESXi, both are free and can provide the virtualization you're looking for. Other solutions exist, but if you're not familiar with them already will probably have a higher learning curve.
A setup like this reusing old hardware is likely to provide poor performance, reliability, and will have relatively high maintenance costs. If it's just a proof of concept or learning environment, this is probably the way to go; otherwise I'd start with purpose built hardware.
Not sure if I understand the question but you wont be able to have high availabilty of your virtual machines running on a host system.
If you're already running an OS, then you need to add on a virtual machine service to windows. this would include: - virtualbox (free) - vmware server (free but being discontinued) - vmware player (free) - vmware workstation (paid)
You can run VMs on each desktop, however you WILL notice a slowdown of the host system even if the VM isnt doing anything. CPU is only one concern - HD activity, network activity, ram, and most endusers will notice if you "sneak" a vm onto their workstation.
If you're looking for high availability - to move vm around from machine to machine seamlessly - you're looking at commercial software from vmare/xen/microsoft.
Using existing workstations is a bad idea as it will be slow and hassle to admin. What you're asking about isnt done in the real world. If you're wanting to play sure go for it, but if this is for a business/school/nonpersonal network it's bad idea to try to harness the "spare" cpu power, cannot stress that enough.
It doesnt scale.