If you're on a budget, you could get an inexpensive HP DL385 G2 on eBay, update the BIOS and put extra memory in it (say 32GB using 8x 4GB PC2-5300P REG ECC memory for instance) and matched 2x quad-core AMD 2356 2.3GHz CPUs (use B2 or higher stepping only for that model of AMD quad-core) in the DL385 G2. Those CPUs with that stepping level have VT and RVI capability and each CPU is about $10 delivered price to USA locations. Then install ESXi 5.x on the DL385 G2 using local drives while booting ESXi off a USB stick.
From there you could create nested XenServer 6.2 VMs running on the ESXi 5.x physical host and get XenCenter running in a Windows VM on your ESXi host.
From there you could run x64 VMs on the nested XenServer 6.2 VMs and do whatever testing training you wish to do.
You could even install a nested ESX 5.x VMs and a VCenter and run nested ESXi 5.x clusters on your physical ESX 5.x server.
That HP DL385 G2 with those processors and memory will also run nested Hyper-V 2012 R1/R2 or if you prefer, Hyper-V 2008 R2. It'll also run nested KVM with VMs running on the nested KVM host if you wish.
A relatively inexpensive but versatile server for learning about different virtualization technologies or testing out various virtualization setups.
Datto
