Rent a digital Mini-DV camcorder that has analog ins, analog pass-through and Firewire out. Attach a VHS player to the analog ins of the camcorder, use iMovie to capture the Firewire DV stream from the camcorder.
Ask the rental shop to explain this and verify that the camera is compatible with this approach.
Otherwise, purchase an video-Firewire conversion/encoding box from a company like Canopus, Elgato or Datavideo, will cost roughly $200.