If you have just downloaded Lion, then you will notice there is already an update available in the guide of iTunes 10.4.
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.