One way is to play the tapes through a 8mm video camera or VCR connected to your computer and using capture and conversion software to copy it and convert it to digital and then burn it onto DVDs. Your computer would need to have a IEEE-1394 interface port (FireWire, iLink). There are conversion devices with software that utilizes the USB on a computer from the A/V ports of the camera. But there are mixed reviews on how well these devices work. I have one cheap one and one expensive on and the costlier one works best ($$$).

The easiest and maybe the cheapest is to take your tapes to a video service center that offers transfer service. One video store in my county charges around $15.00 per tape. Some websites offer the service for less but I would feel more comfortable hand delivering my tapes to a location in my town than mailing them off to who-knows-where.