If u have a free PCI slot, you can go for PCI version of Display Cards. Then you can use both of the cards (Your existing AGP/Onboard and PCI) at the same time.
Get any 8MB PCI VGA card and your low cost dual display is ready to rock.
JetWay's MagicTwin N2View motherboard has 2 moniter, mouse and 2 keyboard connectors.One can use this as 2 computers.It has nForce GPU and also an AGP 8X slot.Performance is acceptable if one user is playing 3D games such as Q3 and the other is using for tasks such as browsing,Office and other non graphic intensive apps.But system crashes if 2 users use graphic intensive games/apps simultaneously.
*www.jetway.com.tw/evisn/product/twin/n2view/n2view.htm