You could try the Unlocker program:
http://www.emptyloop.com/unlockerOther things to try: make sure the Windows file association for that
particular file extension is correct. Try copying the folder containing the
files to another folder, then open them from the new folder. Try copying the
files individually, giving them a different name during the copy (i.e. copy
file1.jpg file2.jpg).
Copy the files to another drive, reformat the problem drive, and then restore
the files. Note that if you were using FAT32 then I recommend you change to
NTFS, it is much more robust and less problematic.
Let me know if any of these suggestions help, or if you figure out an
alternative solution.