iMovie video and audio out of sync

I saw other old topics about this but couldn't find an answer. This problem came up for me today and some of the stuff that happened might help in solving it.

I recorded two video clips simultaneously for a picture-in-picture video, one using the MacBook Pro built in camera from the iMovie camera import window, and one using a bloggie camera. I imported the clip from the bloggie into iMovie, made my picture-in-picture project, and matched up the clips' sound well enough that although the sound was playing twice, you couldn't tell. However, the video didn't match up. The video from the built in camera was 1 second faster than the sound and the other video after a minute, and over 2 seconds faster after 4 minutes, but at the end of the 20 minute video, the two match up again. It's unfortunate cause it'll be difficult to redo and rerecord what was recorded, and I can't think of any simple way to fix this.

Also, on a separate video, recorded from the same bloggie that has imported fine other times, the video in the clip that was imported into iMovie lags at the start, but the sound plays normally, and video and sound are very noticeably off. In this case though, the sound was off by the same amount the whole video so I just used the same audio but played it at a different time and it wasn't a problem.

To me it seems like it probably isn't a problem with sound or with the built in camera, but rather it's a problem that can occur with the video in iMovie. Is this a known problem and is there anything to do to prevent it from occurring?

I'm using a MacBook Pro running 10.6.8 and iMovie 11.

Edit: For the clip with the video off, I checked the .mov file in the iMovie events folder and it has no problem, so maybe I can use that.