Modern Macs cannot be connected to a non-digital camcorder without purchasing additional hardware.
You'll need either an analog capture card or an external analog/DV converter. If you want to use Apple's capture software (iMovie or Final Cut Express/Pro) the external converter is the way to go.
Here's one example:
I would ask you, how much Hi8 content do you have to edit? The reason I ask is the $ for the A-D converter is about $200 and is almost half the cost of a new mini-DV camcorder (which would not need a converter and could be plugged directly into your mac with a firewire cable). Not sure of your situation, but it's something to think about - what to spend to get the biggest bang out of your buck!