Replying to HELP ME with quicktime bug

ok so, since ive gotten itunes 7 and upgraded quicktime whenever i try to play a .mov or .mp4 video file in either quicktime player or itunes all i get is pink static, sometime with green. static sound too. mpeg's play fine though. when i right click and say open with > internet explorer everything plays fine (mov mp4 and mpeg) even though internet explorer seems to be playing them with quicktime. what the hell is going on???? and why does itunes get all distorted if i open a new ie window (even though my cpu and ram arent getting very heavily taxed), and when i have a qt movie playing in an internet window whatever song that's playing in itunes gets horribly distorted. HELP