Apple is now providing Quicktime 7 for Panther (Mac OS X 10.3) users in your Mac OS X Software Update. New features include:
H.264 video support
Live player resize
Zero-configuration streaming
Surround sound
New and improved playback controls
All-new content guide
Quicktime 7 Pro:
Audio and video recording
Simplified movie sharing
Full-screen floating controls
H.264 video creation
Surround audio creation
Concurrent exports
Improved movie authoring
AAC constant-quality encoding
3G streaming content creation
Quicktime Pro users will have to purchase a new Pro software key after upgrading to Quictime 7. Apple has also updated their Quicktime 7 site.
Quicktime 7 for Windows is "coming soon".