Today Apple released the iTunes 10.5 before the launch of iCloud and iOS5 which is expected today or tomorrow. The software update would have notified this update in your Mac OS X or Windows. Here is the download link for iTunes 10.5 for Windows 7 32 bit and 64 bit. Different versions of downloads available for 32 bit and 64 bit Windows.
The major new feature of iTune 10.5 is the iCloud which allows your all Apple devices to download and sync your new and previous purchases such as music, TV, books and movies. So, you will not miss anything in your Apple devices by using iCloud. Wireless syncing through WiFi is another major feature with this release.
More information about new features and security updates about iTunes 10.5 available here.
iTunes 10.5 for Windows Operating Systems gets more security updates, find out the more details about it here.
Select the appropriate version while downloading.