Available in Software Update for around 27.7MB:

iPod Updater 2006-03-23 delivers:

New iPod Software 1.1.1 for iPod
New iPod Software 1.1.1 for iPod nano
For all other iPod models, iPod Updater 2006-03-23 contains the same software versions as iPod Updater 2006-01-10.

Important: After downloading the iPod Updater software, connect your iPod to your computer and launch the iPod Updater application. If iPod Updater determines that your iPod needs to be updated, click the Update button to install the latest software on your iPod.

Features of iPod Software 1.1.1 for iPod and iPod Software 1.1.1 for iPod nano:

Volume limit
Bug fixes

[Update] With this update Apple has added a new function to iPods, Volume limit provides an easy way to set the maximum output volume to prevent an iPod from exceeding this level.

“As the leading provider of digital music players, Apple continuously brings iPod customers innovative and easy to use solutions,” said Greg Joswiak, Apple’s vice president of Worldwide iPod Product Marketing. “With the increased attention in this area, we want to offer customers an easy to use option to set their own personal volume limit.”