You'll need a video card with 2 heads one for each monitor or run two Video Cards the first is the easier as the software for the dual displays comes with the Card.
Now for potential problems you'll have to setup the display well before you even start to consider the presentation as you need to drag different displays to the second screen for them to run so you need to be able to see both monitors as you setup the presentation. This is quite a common thing with the latter generation Dual Head Video Cards and if you do not have space problems by the computer itself it is easy to do.
The second option is to add another Video Card but generally it will display the same as the first Video Card so you'll need extra software to split the viewing area which I haven't seen available for a long time now since the Dual Head Video Cards became so prevalent. Currently I can pick up a Dual Head ATI Radeon for about $65.00 AU and that has 128 MEG of RAM on it but just a word of warning here make sure that the card will actually fit on your M'Board as some of the new 8X AGP cards will not fit in a 4X socket. You can get the same results with a PCI Video Card but they are a little harder to find now days since the introduction of PCI Express which you can not use in a normal PCI socket.
Col