I have two 24" widescreen 1080p monitors.
Most modern graphics cards will have two outputs (mine has 2 DVI out, some are one DVI one VGA - it doesnt matter so long as there is two).
You can either have one start bar on one monitor and none on the other, have it extend right the way across both, or have a 'smartbar' on each which is essentially two start bars, which recognise which windows are on which monitor and show these on the correct start bar.
I use my right hand monitor for games etc, and then have tv/msn/etc open on the other so I can see both at the same time. Ofc if I'm not gaming this means I can have full screen surfing on one and full screen tv on the other, or surf research on one and type essays on the other etc.
I would never go back to a single monitor, its about the best upgrade for multitasking you can get...
Typically I have it something like this:

...where I would either be browsing or gaming on the right, with the start bar acting as a division between the two screens (and it keeps the start bar nice and central so it's easy to get too) with tv/msn on the other (as well as the start bars clock, which is handy).
As an aside with my new PC I will be getting a third 'monitor'. Ill keep these two connected as are, albeit to an SLI setup rather than a single card, then get a third card and plug a 48" TV to it to use as my main TV (through a TV card) or as a monitor when I'm not watching TV. Could also put a switch in to use it for games... If I really felt like it.
Talho wrote:
anyway I dont think you need 2 graphic cards, something that can convert one port (like a switch box) to two ports.
or having vga&dvi (& hdmi) might work also
A port switching box just does the same job as mirroring, you dont get two seperate screens.
One card with either VGA+DVI, 2 VGA, 2 DVI, or DVI+HDMI ports would work.
If your card only has one port you will need either a second card (assuming your motherboard has two slots), or a new card with two ports.
If you want triple screens you need two cards with at least 3 ports, both of which run on the same graphics driver, eg. 2 nVidia 8xxx cards.
You can also do SLI on two cards supporting 2 monitors and get a third monitor on a third card, so long as ALL the cards run under the same driver (which is how my new PC will be set up with 2GTX 280s and one 8800GT).