The cluetip module is a wrapper for the jquery cluetip plugin which can be found here, and downloaded here. The Cluetip plugin provides nice, configurable hover-overs using the "title" attribute. The plugin has many options, and includes a "demo" folder, which you should check out to learn about how it works.
Notes on the D7 version:
For developers considering options relating to including jquery plugins, I know there is a module or two in active development that are working on centralizing these into a registry of some kind so modules don't end up including the same plugin multiple times. As such this module has the following requirements: