Along with Mac OS X Lion¬†and the new line of Mac Minis and MacBook Air, Apple rolled out iTunes 10.4. The new software is designed to work with Lion. It allows for the use of fullscreen along with other features.
Here’s the additional info:
What’s new in iTunes 10.4
iTunes 10.4 is now designed for OS X Lion.
You can now use iTunes with OS X Lion’s new Full-Screen App capability, which allows you to use iTunes and other apps without distractions. Navigate between your full-screen apps with a simple gesture.
Note: iTunes is now a 64-bit Cocoa application on OS X Lion and includes a number of important stability and performance improvements. Some iTunes plug-ins may no longer be compatible with this version of iTunes. Please contact the plug-in developer for an updated plug-in compatible with iTunes 10.4.
You can download the update by clicking on the Apple on the top-left and choosing Software Update.