ITunes and QuickTime are closely knitted together, more so iTunes. You can download and install QuickTime without iTunes, but a certain version of iTunes requires a compatible version of QuickTime.
As always, you can install via Software Update or via a direct download:
What’s New in iTunes 7.1
Using iTunes 7.1, you can now enjoy your favorite iTunes movies, TV shows, music, and more from the comfort of your living room with Apple TV. iTunes 7.1 also supports a new full screen Cover Flow and improved sorting options to let you decide how iTunes should sort your favorite artists, albums, and songs.
QuickTime 7.1.5
QuickTime 7.1.5 delivers numerous bug fixes and addresses critical security issues. This update is recommended for all QuickTime 7 users.
Important Notice for QuickTime 5 and 6 Pro Users
Reminder QuickTime 7 will disable the QuickTime Pro functionality in prior versions of QuickTime, such as QuickTime 5 or QuickTime 6. If you proceed with this installation, you must purchase a new QuickTime 7 Pro key to regain QuickTime Pro functionality. After installation, visit www.apple.com/quicktime to purchase a QuickTime 7 Pro key.