Older versions of FPW Post Thumbnails ( now part of FPW Category Thumbnails ) did not provide turning off display of current theme's thumbnails. The only solution was editing theme's templates to remove or comment out calls to the_post_thumbnail() function ( contrary to author's promise that modifications of the current theme is not needed ). Recent versions FPW Category Thumbnails ( 1.6.4 and up ) finally provide this functionality. There is an option Hide output of the current theme's the_post_thumbnail() in FPW Post Thumbnails. Check this box, click Update button, and it's done. Once set, you don't even need to have FPW Post Thumbnails enabled.
New version of this plugin fixes the thickbox Get Image ID format problems for all versions of NextGen and NextCellent galleries.