Two monitors on one tower with one VGA port?

I have an HP Pavilion with Vista home premium, NVIDIA GeForce 6150SE nForce 430, from what i've researched it's capable of supporting two monitors. The tower only has one VGA port on back and both of my monitors have both VGA and DVI-D ports, I need to know how to connect them all together so that both monitors show up when i go to personalize the display to an extended desktop. I was going to buy a VGA-Y Splitter but from other peoples posts it seem that it only accomplishes mirroring the desktop, and doesn't show multiple monitors in the display options. So basically what I need to know is what type of splitters/adapters will allow me to Extend my desktop across both monitors? Tower- 1 VGA port 2Monitors- 1 VGA ports 1 DVI-D port each