Do you have a DV camera? Most will have the appropriate inputs. There are other ways to do it but in any event you'll need some kind of a device to capture the video. Look here for some ideas.
I use the Canopus ADV100 which hooks into the VCR on one side and to my mac's firewire port on the other side. It was a little pricey, but it works seamlessly with iMovie. The only problem (also a benefit) is that it imports them as DV, so the files are huge. I compress them to MPEG2 files for long-term storage.