ah i see what you are doing but i wish to output to 4 monitors. Each monitor is to have a seperate application running on its own desktop. sorry if i did not make it clear earlier. I have looked at quad head graphics cards but am trying to keep costs low.
Windows really isn't designed to run multiple desktops in that way. Usually (its not really multi-user in that way), the best you can do is have one large destop with an application open and running in each portion. You still have only one keyboard/mouse though so unless your applications are non-interactive you may have problems.
You might be better of with a Linux type OS where you can run multiple desktops at the same time (although I think 4 KDE sessions would push even a fast PC - you might be able to run some of the simpler gui's though)
as said above windows isnt really designed for it - it is possible tho - you've seen my setup lol - would suggest you go for 2 cheap nvidia cards - doesnt matter what really as long as they are twin headers and match your slots - would NOT suggest trying to get 4 seperate cards to give a single desktop each lol - and I really wouldnt want to try with non-nvidia cards lol
utils like ultramon help to keep everything organised once you have the physical hardware running
the cost of the graphics cards is negible compared with the cost of the screens and mounts lol
i know on one of my old motherboards you could add something called a riser card that quadrooples the amount of slots you have lol. i had one slot, cant remember what kind, but the old graphics cards used to go in them, after putting the rise card in i could put 4 graphics cards, not that i did.