hi rd08!
hmmmm. the 6344x's can be a bit fiddly to troubleshoot. (people sometimes report seeing 63441 or 63440 in this context.) we're going to start out simple, and get more aggressive if the simple measures don't work for us.
first let's try a careful standalone QT 7.0.4 reinstall.
download and save a copy of the QT 7.0.4 installer to your hard drive. (we'll run the install from there rather than online.)
switch off all antivirus and antispyware applications prior to the install.
Quicktime 7.0.4 Standalone Installer
if the install goes through okay, do your itunes and QT launch properly again?
if you get an error message on the install, let us know what it says. include error message numbers if you're getting any.
love, b