You need a video card with an analog video input, such as the Radeon 64Mb VIVO, or you need to buy a 1394 card(also called a Firewire card or iLink).
I have both and the Firewire card is the best option IMO. I got one packaged by ATI for $50USD. It came packaged with ULead 5.0 a popular basic editing software package. I have no complaints with the setup.