Dual Monitors has been about the best, and coolest tweak, I've ever added to a personnel computer.
It's simple to do and makes really good use of the "old door stop" computers. An old 486 or Pentium that is less than
233 MHz is practically worthless.
Monitors can be expensive to buy, so why not re-cycle the monitor from your old PC?
Maybe the video card can be used as well?
Usually any 3-d gamers card will work. ATI
Rage is a good one. This setup will not work with most 3-D games like Quake, since the game does not know
which card to run on. So you just un-check the box, "extend my Windows desktop onto this monitor", and play your game.
On a newer Computer, most have a "dedicated" video slot. You can always tell, it looks like a PCI, but has a "hook" on the card. It positioned slightly different too.
The second card is ALWAYS a PCI type card.
You can get one card to run dual monitors now, though these are
expensive.
To the right is a 1.5 GHz Dell 8100 type personnel computer with a Sony Trinitron
21' Black Monitor and an older 17" Dell "plug & play".
The first video card is a 32 MB DDR ATI Radeon 4x AGP video card. The second is a
16 MB nVidia Chipset.
Try to mix brands
Having the same brand name of cards has caused problems.
Here is what pops up when Windows recognizes the dual monitors. Notice the properties for the smaller, secondary monitor/video card.
notice the checkbox towards the bottom-left, "extend my Windows desktop onto this monitor".
To find out more, search your computer for display.txt, or read it here.
This has some older information about dual monitor setup.