jpg transfers between Nikon/PC/Drive/Mac

Not sure if this is the proper area to post, but it has to deal with photos, so I'll give it a shot...
On vacation last week, I downloaded photos from my Nikon to my wife's PC. (I normally bring my MacBook, but thought I'd leave it at home this time.) My wife then transferred the files to my Verbatim CLON portable drive. (I usually use it with my PowerBook). When I plugged the Verbatim drive in to my MacBook to retrieve the files, they weren't there.

My wife says they were there when she checked them earlier in the day.

Any idea where they went? Is it possible that my MacBook couldn't see the files since they were copied over from a PC?

Any help would be great.