um it should have come with a cable or dongle thingy, that splits ur S-video out into three or four things (your standard red, yellow, white, S-video). you should just plug that cable in, and that should be able to take input signals to your computer,and output signals to your tv as well. (ViVo= video in Video out) here is what it might have looked like.
but your gfx card should have come with a program (like if it's an ATI, it would have had ATI TV or something) so you can use that feature. but if you didnt install the drivers for it, then it probably wouldnt wrk either. also what kind of gfx card is it?
check with ur manufacturer or on the box it cam in, to see if your card model has ViVo capabilities.