Q: keep getting a sign stating that I must have quicktime to play my videos when I already have quicktime downloaded. So why won't the videos play?

I downloaded the newest version of the itunes, but I had to delete the old one and quicktime. So after I downloaded the new itunes I downloaded the Quicktime 7 so I can play my videos, but I get a message stating "This movie requires Quicktime, which is installed but failed to initialize. Uninstall quicktime and reinstall it." I've done it twice. I also get a message stating "itunes.exe has been to run in compatability mode for an older version of windows. For best results, turn off combatability mode for itunes before you open it." The system that I have is XP and it's on the list of programs that it functions with.