1. Take off the side panel, check if you have PCI-E x16 slot. Or look the spec of your model on gateway website. 06 is not that old. Some older models use AGP instead of PCI-E.
2. Buy a cheap video card with 2 outputs. Geforce 7200, 7300 are good enough in your case. You can often get those free after rebate or
3. After you install the driver, click on properties and select extend desktop to 2nd monitor.