if you look inside the playback buttons.txt file that comes with my latest samples, there are instructions that show you need to create image objects rather than just use the filename when creating your buttons.
//if you want to change the images, uncomment these lines below and modify the paths accordingly
//do not use fb.FoobarPath here as fb.ProfilePath already points to the same location if using portable mode
//b.images.stop = gdi.Image(fb.ProfilePath + "my_theme\\images\\stop.png");
//b.images.play = gdi.Image(fb.ProfilePath + "my_theme\\images\\play.png");
//b.images.pause = gdi.Image(fb.ProfilePath + "my_theme\\images\\pause.png");
//b.images.previous = gdi.Image(fb.ProfilePath + "my_theme\\images\\previous.png");
//b.images.next = gdi.Image(fb.ProfilePath + "my_theme\\images\\next.png");
so you can just add your own hover image...
b.images.stop_h = gdi.Image(fb.ProfilePath + "path\\to\\stop_h.png");
you can use p.ip in place of fb.ProfilePath + "marc2003\\images8\\" if you need to.
then you can use it when creating your button...
new button(0, 0, bs, bs, {normal: this.images.stop, hover: this.images.stop_h}, function() { fb.Stop(); }, "Stop"),