Anirudh Pal

It is possible in other simpler ways, using Windows MultiPoint server on the main overkill PC, and then connecting something called Zero Clients, they look like the following, and would allow you to produce the following setup.

There are multiple models, some cheaper than others, the cheapest model is I believe about $20 each and then they is also a more expensive model which has 4 USB ports, no PS/2 and it's own ethernet jack. However there is no need for the more expensive model unless you won't be using PS/2 or you need more USB ports. These thin/zero clients also only connect via regular USB ports. Although the software is expensive, and you need to buy individual CALs or user codes I believe.
 
EDIT: Also this is probably the most cost effective.
 

Possible, virtual machines with remote connections from weaker PCs over LAN.

Softxpand on Windows does this EASILY

go read this
http://en.wikipedia.org/wiki/Multiseat_configuration
 
it's been explained in here
http://www.reddit.com/r/buildapc/comments/1wqbhu/can_two_people_use_the_same_computer_at_the_same/
 
anyway it's not really uncommon in my country, the problem is, setup probably lot's more complicated
I've seen and use these kind setup in all McDonalds, common problem for me
1. Resoultion is limited to 800x600/1024x800, and it only could be change from main computer
2. it doesn't support 3D Hardware Accelerator, so no flash, no 3D games, no Render
practically useless if you want make the client side a workstation except you doing multisheet/document
 
Although lot's of improvement (from software developer log)
with new launch intel/amd mini pc/pico pc/soc solution with very low power usage for based to mid usage (about 5-20w) this multiseat config no longer be an option nowdays, people also prefer staring with their tablet/phone on public resort.
 
you can try free trial here: http://www.miniframe.com/products/softxpand-2011-duo.html?resource=Technology

IOMMU, totally possible
 
 
so,
step 1) ensure your hardware is AMD-Vi/Intel VT-d enabled. if amd, easy. its got like a 99% chance of having it. intel, check ark
step 2) ditch windows as the base OS. its time to dive deep into linux
step 3) you need libvirt, qemu-kvm, and virt-manager
step 4) setup linux host for PCI-Stub. you need to have various GPUs claimed by PCI-Stub.
step 5) create windows VM, get it set up and working. then clone it.
step 6) add devices to VM. GPU that is claimed by PCI-Stub, keyboard, mouse. remove VNC display, remove VGA display.
step 7) start VM back up, and it should now have its own keyboard,mouse, GPU, etc.
rough instructions, but there you go. multiple GPU accelerated VMs on a single power house system

Okay here is the idea:-
1) U make a really powerful over-kill PC.
2) Connect several Stations( each including a Monitor, Mice, Keyboard & USB Hub).
3) Have multiple users access and work on things at the same time from their respective stations.
4) HOW DO I MAKE THIS HAPPEN???
 
Note:-
The operating system has to be Windows as these are 3D design workstations using software that only works on Windows.