Theme Fur is a quick'n'dirty converter that will "fur" your themes - in other words, it will allow current themes to work with Jaguar. For the tech-inclined, this software copies your current Jaguar 'Extras.rsrc' file into a new theme and then overwrites Jaguar resources with your themed version. Only 'ppat' and 'pxm#' resources are overwritten. This means that some themes that change the layout of various interface widgets will still need to be manually updated by their authors. Izawa's themes in particular will have this problem. All resources get the name and attributes of the Jaguar version.
I don't have a copy of Jaguar, so this software has not been tested very thoroughly. Feel free to let me know if there are problems.