iOS 4.3 isn't expected until March 11, but Apple has already pushed out an updated version of iTunes to handle synchronization with devices running the new platform. iTunes 10.2 not only adds sync support for iPad, iPhone and iPod touch units running iOS 4.3, but updates the Home Sharing support on Macs and PCs.
Home Sharing will allow iTunes to stream music from a PC or Mac to an iOS 4.3 device, with support for browsing the full catalog remotely. There are also various security updates for the Windows version of iTunes, more details of which are here.
iTunes 10.1 is a free download, and you can find more information here.