I am currently running Win Xp with 3 monitors.
I've got 2 monitors running on an agp video card with dual outputs and the 3rd monitor is run by a pci video card. the set up works quite well and is very easy to do. any time you have multiple video outputs available with multiple monitors plugged into them you can then run whatever apps you want on whatever monitor you want. Windows knows how many monitors you are running and that they are indeed separate monitors that should also follow if you have a projector plugged into a monitor plug. when running full screen apps they will display at full screen on whatever monitor you put it on, so for your PP presentation you would be displaying it at full screen on your projector and still have your regular desktop on your other monitor(s).
I also use a small program called
ultramon to help manage how I want things to display on the different monitors. it gives added control over your task bar screen saver and desktop wallpaper among other things.
Hope this helps feel free to ask more questions if you have them. I'm pretty handy with multiple monitors. once you have 3 you'll never go back to just 2!
And then you will wrack your brain trying to figure out where you could squeeze in a 4th!