I imagine OP means mini-DVD, and I think OP is using an external drive to look at them.
OP, what is the format of the movie file (what is the extension?
Copy it to your desktop (just one of them) and change the extension to .mpg. See if you can open it in Quicktime and play it. If so, you'll need to transcode it to .dv or .mp4 for iMovie to play nicely with it.
What version of iMovie and OS X are you running on?