There are some software programs you can buy to do this but you'll also have to buy a dvd burner if your computer doesn't already have one. A good one would cost between $100-$150. The best and least expensive way to do this is to check your local yellow pages for a video conversion service. I found mine by looking under DVD, Video Tape Duplication Services.
If you choose to do it yourself, I would recommend checking out Pinnacle Studio. You can transfer the tapes to Pinnacle, edit them, and save the file to your computer. Then they'll be ready to transfer to a dvd.
Hope this helps.