I have been using Safari for a couple of years on this XP computer, this morning it failed with the message: "Safari can't Open. Your copy of Safari is missing important software resources. Please reinstall Safari."
I uninstalled, and used my download to reinstall, failed. So, I uninstalled, and rebooted, and downloaded a new copy SafariQuickTimeSetup.exe and reinstalled.Failed again. All other software is working fine.
That suggests you were having a problem with your Apple Application Support, rem. (There was a higher version of AAS for iTunes + QuickTime than there was for Safari last time I checked, so the iTunes install would have updated your existing Apple Application Support.)