I have read other people's questions/answers and saw that many people's problem were resolved when they installed the latest version of Quick Time, so then opened Quick Time and looked for updates and it said that none are available and my software is up to date.
Yeah, the QuickTime-related launch problems appear to have been fixed in the 11.0.2.x versions. (I've just stopped seeing new cases of them being reported since the release of the latest version.) So something else is likely afoot if you've got the most recent iTunes version.
In the course of your troubleshooting to date, have you worked through the following document?
Another problem I'm having (not sure if they are related) is that when I restart my computer it tells me that the Apple Sync notifier cannot be found.
With that one, try uninstalling your MobileMe control panel.