I don't know much about TXT, but VT-d is great! Like mentioned above it allows hardware devices to be assigned directly to a virtual machine. From the VM's point of view, it is like the hardware is directly plugged in.
My use case for wanting this technology was to setup a virtualized multi-seat computer. I wanted to setup multiple VM's each as their own separate workstation, and I wanted them to have the speed and power of non-emulated 3D graphics. I.e. two or more separate gaming VM's running from the same physical box! With each VM having it's own monitor, graphics card, keyboard and mouse.
I've got two seats currently setup on my machine. Please be aware that it is non-trivial to setup and maintain. You also have to be careful with the make and model of your CPU, Motherboard and the BIOS you choose for the setup, as they all have to support VT-d for it to work. I've got it to work with the following hardware and software.
- Intel i5-2500 (non-k)
- AsRock Extreme 4 Gen 3 Z68 Motherboard
- ATI HD 6850
- ATI HD 6450
- 16gb ram
- 1tb storage
- 3 x Monitor/Keyboard/Mouse (the extra monitor plugs in to dom0)
- Dom0 - Debian 6, custom 3.1 kernel and Xen 4.1.2
- 1st DomU - Win 7 Home Premium
- 2nd DomU - Win 8
My setup isn't exactly the same as this guys, but check out the clip for a demonstration of what I'm talking about: http://www.youtube.com/watch?v=Gtmwnx-k2qg