JQuery plugin

Yep, you can add any jQuery plugin you want.

What you need to do is add some code to the template.php file of your theme (or, alternatively, manipulate the .info file of the theme) to add the appropriate js file that contains your jquery plugin. For example, something like this would suffice:

drupal_add_js("misc/portable_unit_converter.js");

You can also add this line to the page.tpl.php file if you'd prefer, or pretty much any theme file you want for a more specified inclusion.

Spiro