Need to replace spaces with underline character in image filenames

I have hundreds of image files in my site and an awful lot of them have spaces in their names so they fail the File/Validate.  I could rename them outside of DW using a windows cmd line rename. but then all the pages referencing those files will fail as their code retains the old names.  I have to somehow do it within DW so DW pops up with "update links in the following files?" prompt and goes off and updates all the references.  Currently I am manually using Edit/Rename in the Files panel, changing the spaces to _   I'm confident its not possible! - please prove me wrong 🙂