Check Software Update on your Mac for the latest update to iTunes, preferably before you update your iPhone, iPad, or iPod Touch to iOS 4.3 so you can get maximum compatibility.
Straight from Apple --
• Sync with your iPhone, iPad, or iPod touch with iOS 4.3.
• Improved Home Sharing. Browse and play from your iTunes libraries with Home Sharing on any iPhone, iPad, or iPod touch with iOS 4.3.
For information on the security content of this update, please visit: support.apple.com/kb/HT1222