If you are using Mac OS X 10.3.9, QuickTime 7 will appear in Software Update as an available download. After installing it, your computer will restart. If you have Developer Tools for Mac OS X 10.3 Panther installed, and wish to continue using using the QuickTime SDK (Software Development Kit) after you have upgraded to QuickTime 7, you will need to download the QuickTime 7 SDK.
You can do this by running Software Update again after installing QuickTime 7. This will make the SDK available to download.
If you don't run Software Update manually at this point, the QuickTime 7 SDK will automatically appear in Software Update after a week (if you're using the default "Check for updates Weekly" setting in Software Update Preferences). If you want to get started with the SDK sooner, make sure that you manually run Software Update.
To learn more about the QuickTime 7 SDK or to manually download the update, please visit the QuickTime section of the Apple Developer Connection site.