By pluging your pc into the TV you are only replacing the monitor, so therefore any mouse, keyboard, joypads etc you use on the pc stay connected to the pc, but the picture is on the tv not the monitor

Most new 3d cards have tv out now, even cheap ones, however you will most probably need a cable to convert S-Video out to SCART. If your TV or VCR doesn't support SCART then chances are you won't have much luck converting it to an arial input. If your 3d card doesn't have a tv out socket, you can pick up a cheap gf4mx card with tv out for around £60, or if you are happy with the 3d card, some PCI TV cards will allow TV-out, even whilst using 3d accelleration