WordPress tooltip plugins lets you add tooltips to plain text and links on your post and pages.
It offers a tinyMCE shortcode GUI which will guide you through the entire process of a tooltip.
This plugin uses jQuery tipTip authored by Drew Wilson http://code.drewwilson.com/entry/tiptip-jquery-plugin.
You can also add tooltips manually by following the pattern below:
[tooltip content="This will show in a tooltip" url="This will make tooltip a link"]Hover over me for tooltip[/tooltip]
Url is optional. If URL is added, it will render a link otherwise it will be a plain text.
Dieses Plugin steht zum Download zur Verfügung, um in deiner selbst gehosteten WordPress-Installation verwendet zu werden.