Projects containing DV media files captured using versions of Final Cut Pro prior to version 4 may take significantly longer to open. This is expected behavior.
When opening or importing DV media files captured with Final Cut Pro 1, 2, or 3 into Final Cut Pro 4, you may notice a slight delay for each file. This delay is due to Final Cut Pro 4 validating the audio sample rate of each media file to ensure that audio/video sync is maintained. DV media files captured using Final Cut Pro 4 have this adjustment applied during the capture process, and stored permanently in each media file.
This delay is different than the project updater that runs the when an earlier project file is opened in Final Cut Pro 4 for the first time.