At last I can import vids from my Panasonic DV camera straight into iMovie on my Intel-powered iMac with Firewire 800 ports. I bought a F/W 800 cable, which refused to work at all. I had to resort to importing the vids into iMove 06 on my old G5 iMac with F/W 400 ports and copying the files across to the new Mac for editing etc.
I have just upgraded to iMovie 11 and the problem still existed, so I thought I'd blow a fiver on this converter plug which has a F/W 800 male connector on one end that plugs into the back of the Mac and a female F/W 400 socket at the other end into which I plugged my old F/W 400 cable that worked on the G5 iMac. Bingo, it worked!
So much for the apparent backward compatibility between F/W 800 and 400.