Can't Open JPEG Files from a Mac

I've transfered some JPEG files from a computer running Mac OS X, but I've tried several image viewing programs and cannot open the files in any of them.

In Windows Picture Viewer: no preview available

In Photoshop: something about wrong marker type

In Nero: Unsupported file format

I copied them onto a flash drive, but when I put them on the PC, each file had another file that was the same name but with a ._ attached to the front.

Both of the files have data in them, one has much more, but they both have data. My thinking was that the ._ files had the header information or something.

Any suggestions on what to do about this?