The idea of having a small footprint hypervisor as the primary OS on a laptop or desktop where every "real" OS is a guest appeals to me. Now I realize this software is more typically used on blades and the other servers but can it be done on a normal PC? Should it be? What requirements are there (eg hardware/BIOS/chipset)? Is there a performance impact for doing so? Is it a good/bad idea?
Hardware compatibility aside the biggest problem with your idea is the fact that the VM's in an ESX\ESXi system do not have the ability to interact directly with the console display\keyboard\mouse on the ESX\ESXi server. You will be left with access only to the ESX Service Console which is a modified RHEL command line environment (or to even less than that with ESXi). To access the user interface on the VM's you need to connect to them over a network using VNC\RDP or some other remote console protocol. This is because these are bare-metal hypervisors - they do not directly provide a VM user interface.
Products like Parallels, VMware Workstation\Fusion, Virtual Server, Virtual Box and the others are hosted hypervisors that allow you to switch between VM's and interact with them because they leverage the user interface of the boot OS to handle the redirected display and user input devices of the VM's.
A really easy way to find out is to create an ESXi USB stick, assuming your laptop will boot from USB. If it works, awesome! Go find it some storage and see how it goes.
If not, you've only lost 15 minutes of your day. The best bit... you haven't trashed your laptop in the process (unless you wipe the drive to become a datastore).
Obviously, performance likely won't be stunning, but it might be Good Enough(tm) to test one or two VM's. That said, I run a half dozen VM's reasonably well on a single CPU/single core desktop PC with 3 GB of RAM, booting ESXi4 from a USB stick (used to get around a weird SATA controller quirk). Horribly unsupported configuration, but works great for a lab :)
Yes It is possible, but I wouldn't recommend it.
ESX is a embedded hypervisor and the way it works is it takes over the whole disk drive so it will erase everything on the disk drive. If you wanted a hypervisor tool to have virtualization then you should use something like VMware Server so you can share your disk drive since it is not an embedded hypervisor
If you run the ESX hypervisor on your desktop, you're essentially running a small linux distro.
At that point, it would be kind of hard to use it as a desktop, so by definition it becomes a server. I know there are some desktop virtualization products coming out, but I don't think we're quite there yet as far as that technology goes. :)
Cletus, I'm not sure I understand the problem you are trying to solve and why isn't handled adequately by the freeware tools from VMware, Microsoft, Xen, whoever that are designed to run as apps on top of a host OS? The Host OS could be a bare minimal install with no un-needed apps, so it comes as close as possible to your requirements but is actually useable.
Even if its possible (ESX, as is said already, has a quite exacting HCL) then I'm not sure its a good idea unless you're talking about a "portable blade" you can take to demos with you and where you'll never need to open a console desktop to any of the guest OSes from the host. Good luck with that one ;-)
Which still brings us back to why not the more "conventional" tools for this kind of task because I can only imagine ESX on a laptop as being about as much fun as using a chainsaw to try and clean an angry bear's teeth.