AWS and Filesystem

In the example for nahttp_fs where the user can store files in the unit I can upload files and they are saved with the correct file extension. When I shall save the files to the computer the files will be named with an .PICT file extension. This will just happen in browsers that comes with Win2000 and Win XP. Win 98 will save the files with the correct file extension. What can I do to make the files have the correct extension when saving them from the unit?