Programming using jQuery is more fun than protoype.js, but Ruby on Rails depend on Prototype.js and script.aculo.us strongly. jRails is solution that use jQuery on RoR platform but jRails doesn't have some plugins, auto_complete, in_place_editor and so on. So I release jrails_auto_complete rails plugin.
% cd /path/to/rails_app
% ./script/plugin install http://svn.raku.to/throwaway/jrails_auto_complete/
Basically, usage of jrails_auto_complete is same as auto_complete plugin. But some options isn't supported yet. For details, see jrails_auto_complete/lib/auto_complete_macro_helper.rb.
This programm is depended on jrails. First, you need to install jrails plugin.
I can't test it enough. If you found the bugs, let me know.