I decided to go ahead a release my FancyBox Gallery plugin as-is. Version
0.1 is very bare-bones: there are no options that you can set. Once you activate the plugin, thumbnails generated by the standard WordPress gallery shortcode will be handled by FancyBox. This works best if you use the link=’file’ option (see the documentation for more details). I’ll eventually add user-settable options for more control.
If you’re interested in trying it out now, download it from the WordPress Plugins Directory: FancyBox Gallery