This is a really simple thing to do in Windows.
you can have as many monitors as you have video outputs on the back of your machine. these can be all the same vga connectors(three lines of dots that you screw in, often blue coloured) or the newer digitial dvi connectors (that are often white). The connection points on the pc can be on the same card or on different cards. it doesn't really matter.
If you want to add more video cards, then simply stick another one in to a spare slot. ebay will have loads of cheap pci cards.
when you turn your machine on, windows will install the cards drivers (or more likely you will have to download and install the cards drivers). Once this is done you can go in to display properties -> settings, (the place where you change screen resolution and screen saver etc) and arrange the monitors how you want them.