There are a few solutions.
One is to use an ATI Radeon card with Avivo. S-video and RGB video input were standard on the more high-end Radeon cards in the X1000-era. I'm not sure if they still have it today, to be honest. You could look into the specs of a few Radeon cards and see if there's one with video in, in the pricerange you're interested in.
My brother used a Radeon X1800XT, and later an X1900XTX to capture video.
Another is to use a separate video input card. Eg the Terratec Cinergy series is quite good. Before he had a Radeon, my brother used a Terratec Cinergy PCI card.
Something like this:
http://www.terratec.net/en/pro...che_daten_en_4392.html
It's a TV tuner card, but it also has direct s-video input for eg a VCR.
Another popular brand for TV tuner/capture cards is Hauppauge.
I believe XFX also has a selection of TV tuner/video capture cards.
Just make sure it has an s-video input rather than just the cable/aerial coax input. Although... technically you could even use the coax input. A VCR will generally have a TV modulator, so it can just output a coaxial signal. It will just degrade quality, and it's a bit more difficult to set up, because you have to tune the TV tuner to the channel the VCR broadcasts on.
For software you could use something like WinDVR. Most cards have such software included. It's very easy to use. Almost as easy as a VCR. Just select the input device/channel and hit record