Apple has released iTunes 4.6.
The new version is required for users to take advantage of Apple's all-new AirPort Express product, which allows Mac and Windows users to wirelessly stream music to a stereo or powered speaker system.
Apple says the software update "also includes a number of other minor enhancements". The update is available through mac OS X's Software Update.
System requirements for Mac: OS X 10.1.5 or later (10.3 required for AirPort Express); 400MHz G3 processor; QuickTime 6.2 or above; 128MB RAM.
System requirements for Windows: Windows XP or 2000; 500MHz Pentium class processor or better; QuickTime 6.5.1; 128MB RAM; Latest Windows service packs.