Prevent file renaming
There are two ways you can do this:


The Upload File Replace module. A small utility module that automatically stops Drupal from renaming new files upload via filefield CCK. When 2 files with the same name exist, the older files will be renamed.
Specify an optional subdirectory within the field setting where files will be stored using a unique token in the file path settings. (e.g. [current-date:raw])