|"...can I plug another monitor into the S-Video port and have triple monitor?"|
You can do that only if
- you can have three displays - in most cases when the video has two monitor ports, you can connect two monitors, OR one monitor and an S-Video or composite connection, but you can't connect all three.
- the monitor has a S-video input port, and/or a composite video input port (a single female RCA jack, usually yellow, usually beside two RCA jacks for audio, usually red and white) and you use a standard S-Video to composite adapter (4 pinsto a female RCA jack) in the S-video port.
A computer monitor doesn't normally have those, but a TV, or a combo monitor/TV might.
However the S-Video and composite output is processed through a TV-Out chip to conform to relatively old and crude TV display standards - the display will look relatively crummy in comparison to the display on a monitor.
If VGA to S-Video adapters exist, I have not noticed whether they do or not, I doubt you would want to use one for that reason.
In any case, you CAN get yourself a hardware video splitter box, connect that to one monitor port, and connect two or more monitors to the box, the displays being identical for the monitors connected to the box - VGA boxes are cheaper, starting at about $35, and you'd probably also need a cable between the monitor port and the box (they usually don't come with it).
OR you can get a USB video adapter and connect another monitor to that.