Thanks for telling us the solution. This ought to go into Dan's "
Unofficial iMovie FAQ", as several people in different places (iMovie Discussions, MacFixIt, etc) have said that a clash of FW ports on PowerMacs can prevent proper importing.
[..My beloved and I spent a few hours on Manhattan Beach one chilly January a few years ago (2001..?) between flights in from New Zealand and back home to the UK. Then we couldn't find a taxi to get us back to LA Airport, so we went to the nearest shop which was still open - a hairdresser, about to close, and phoned for a taxi from there. Brrrr.. Chill-eee!..]