Is the Mini-DV a tape? If so, then you can only get the video off of it via iMovie and then only via Firewire. The Mini-DV tape will not mount as a drive and the extraction process must be controlled by iMovie. There may be other ways to do it, but none that I have found so far. If the Mini-DV is a small CD type disc, then I have NO idea.
Assuming the Olympus has a flash Card in it, then it should be USB only, and the card should mount on the desktop as a hard drive. You can drag the photos off, or use iPhoto to import them. I do both with my Nikon D50 (which is USB only btw).