QT 7 has H.264 video compression, amazing responsive live player resize, up to 24-channels of sound and all new playback controls. Requirements: Mac OS X 10.3.9 or later.
Just in case you hate QT 7 or it does something strange to your Mac, you can revert to Quicktime 6.52 by using the Quicktime 6.5.2 reinstaller that Apple has thoughtfully provided.
"The QuickTime 6.5.2 reinstaller will remove QuickTime 7 from a Mac OS X 10.3.9 system and restore QuickTime 6.5.2. Note: This reinstaller will only run on Mac OS X 10.3.9. "
[Thanks for being up so early, Rob!]