JPEG turned into MP3

How are you searching for the files? Mac OS X's Spotlight needs to index your hard drive before you can conduct a search and this index could take an hour or two (the first time it is run). Also, Spotlight doesn't search everywhere. You may want to try the freeware program EasyFind that you can download from a site like VersionTracker.com (in fact, I've provided the link to the download right below).

http://www.versiontracker.com/dyn/moreinfo/macosx/8707

As far as your previous picture files now being MP3s, that couldn't happen unless the transfer from your PC somehow got corrupted. Therefore, if you can't locate your original pictures using EasyFind I think you'll need to go back to your PC and transfer those files once again. Of course, it is possible that those picture files that you thought you had on your PC were corrupted while on the PC, so you probably need to check for that possibility also.

I believe that this can and does happen - several posters over the years (myself included) have reported that the file icons mysteriously change to another application, and that the "old" file now opens (or tries to open) in this new manifestation.

I'm no expert, but I believe it has to do with data in the resource forks: the LaunchServices database may be the issue.

See my post here for more information, and a link to a potential solution supplied by Dr Smoke.

+*The problem is that some of of my pictures turned into MP3 files, so I cannot read them... when I open those files, they play parts of an audiobook I used to have... and I cannot find the original files anywhere!!!*+

This isn't really an issue with an icon changing or an incorrect application association. If they were jpg files that just changed to mp3 files (with an associated icon change), OS X would just get confused trying to open them. In this case, audio is actually playing. So, it is not just an icon or file association problem. These are actually audio files and OS X sees them as such. I can't really see how this would happen as a result of a migration. I could see files being corrupt and simply not working... but I'm not sure how this would happen.

Carol... if you go to the machine with your original jpg files and try to open them there, are they opening properly?