I have seen an aquaintance use 2 monitors and was able to move the mouse from one to t'other while zooming in on photos, how he did it I know not but his set-up was an impressive - if bewildering array of cables, wires, power stacks & much other stuff that mystified me.
It's relatively straightforward, but do remember that you need to have either two video cards - by whatever means - either two separate cards, an additional USB plug-in, or if you're lucky, a proper dual monitor video card.
These should all come with dual-monitor instructions, or follow the Windows guidelines.
Bear in mind that depending on the processing intensity of what you wish to display, your PC still has to do the initial processing, so even if the video cards are super fast, you still have a processing bottleneck in your PC. This may or may not matter depending on what you are trying to do, but could cripple things.
For simple research and page display there shouldn't be much hassle for text and static pics.
My favourite application for the dual monitor trick was Flight Simulator, with the view on one monitor and the flight instruments, data and comms on the other. This ran almost acceptably on single Pentium III and IV desktops with fast video cards, so I can't see much likelihood of simple research display being a problem nowadays.
If you have a large enough monitor, and Firefox, you can use a split browser, and have multiple pages open on the same screen:
Meant to say, there is another way to achieve a similar trick.
The following allows you to have a number of applications open a desktop that is larger than the your screen, so you can pan between a number of open applications.
Easier to look at an understand what this means than have me try and do it in lots of words, so you can see this one here:
The aerial photos that I was looking at last week were on a PC using two screens. One should have had the GIS system running but the aerials layer was missing so I had RCAHMS Pastmaps on there and then moved the mouse over to the over monitor to select the image I wanted (or at least to try and find it!).
I don't think it was hear but I read someone recently saying they used three monitors on their PC.