If you take a look at this ATI Radeon 9600 AGP (Accerated Graphics Port) card you will see 2 monitor connections.
One CRT (ordinary monitor type)
One DVI (flat panel monitor type)
I you have 2 monitors of the CRT type, don't worry. You can purchase, and in some cases, comes with, a DVI to CRT adapter.
This particular card is for motherboards equipped with an AGP slot. Most newer motherboards (within the last couple of years) have this slot. It's brown in colour and at the top of the PCI slots on the motherboard.
If you don't have an AGP equipped motherboard, you can buy a PCI Video card that has the same setup for dual monitors.
If your PC has onboard Video, just buy a PCI Video card and this will give you the second connector for another monitor.
Cheers!