Shot in the dark: Might try capturing the HDV material using the intermediate codec… that way it’s captured with all i frames. Maybe sync would clean up…?
Post more about the source machine, and the camera that shot the footage (might work best using the camera that shot the footage as the source machine. Also post which version of FCP, OS, and QuickTime you are running.
Do you want an anamorphic output or a letterboxed 4:3? if the latter, put the sequence in a standard DV 4:3 sequence, render it, and then record to your camera.
Try running Disk Utility and disk first aid on it. If that fails, and an erase (reformatting it Mac OS Extended) doesn’t work, I’d suggest that something is wrong with the disk… Might call LaCie about it…
FCP 4.5 can’t capture HDV and edit with it… but with a plugin from Lumeire you can edit captured footage with 4.5.. however you’d be miles ahead upgrading to FCP5 to work with HDV I’d think.