Hi 8 will not have firewire on it. You might try this....connect your Hi 8 camera to your digital video deck/camera. Use whatever you have, s-video or RCA. Then conncet your digital deck/camera to your Mac by the firewire. Then change your FCP capture setting to non controllable device. Then hit play on your Hi 8 cam and hit capture on your Mac. That should work.
I find a better workflow is to dub the analog video to DV tape first. Then you can capture it over firewire with full deck control and repeatable timecode. If you just send it over video in you'll get a clip in FCP with no corresponding physical media. So if you do an edit and somehow the project becomes corrupted you have to start over rather than just go back and rebatch capture the tape.
I agree with Noah, it's best to simply capture to Mini-DV first.
If you want to take analog directly into FCP (it won't save you any quality vs. DV tape), you'd have to get an I/O interface. Don't know what's on the Blackmagic and Aja cards these days.