Home Virtualization Server [closed]
If you are planning on buying hardware to do this, then it is quite possible to buy hardware that will run ESXi, quite cheaply (I did it a couple of weeks ago). There are a number of sites out there that deal with what whiebox configurations work with ESXi such as Ultimate Whitebox
If you have a machine that has enough resources any of these options should work fine, but you may find that ESXi is the most efficient as you don't need to deal with an underlying operating system (other than the ESXi components).
VirtualBox. I've found it to be the most lightweight for home use. You're right about ESXi, the hardware requirements are specific. I'm not a big fan of what VMware did for management of server 2.x either despite my love of them in the enterprise.
AMD's equivalent for Intel's VT is AMD-V however the Sempron line does not support this. So any virtualization that you do will need to support running on hardware without virtualization support.
Xen will do this if you're running paravirtualized guests. But it will only support HVM (fully virtualized guests) if your hardware supports virtualization. Virtualbox is also able to do this but where Virtualbox shines is desktop virtualization. I wouldn't use it for server applications in its current form. I'm not familiar enough with VMware's products to know which will work and which won't or what conditions apply. But Hyper-V requires Intel-VT or AMD-V capable hardware.
If your serious about wanting to do virtualization I would suggest investing in newer equipment that will support it better and get cram that computer with ram if you plan on running many machines.
I use KVM both at home and at work, because:
it is included in the mainline linux kernel (no patching or stuffing around or being restricted to a particular kernel version),
combined with qemu it supports para-virtualisation on CPUs without hardware virtualisation support,
it is feature-wise roughly on-par with all of the others already,
and, most importantly:
- it is the future direction of virtualisation under linux, where the bulk of the development work will be done (e.g. Redhat has just committed to KVM in a huge way)
in the short term, it probably doesn't matter too much, though, because all of the higher-level virtualisation management tools on linux use libvirt which has lower-level interfaces to KVM, QEMU, Xen, VirtualBox, and some others. VMWare is the odd one out here.
whatever you choose now, there are tools to convert from one virtualisation type to another if you decide to change later.