Turn off hardware acceleration for Quicktime in the QT system control panel. that aside, this may be unavoidable compatibility issues. For all intents and purposes, your system is just old, old, old and eitehr QT or the latest Avid CoDecs may use some system library that just doesn't work properly on XP.
I'm mistaken, Animation files don't work either!
I tried that with no luck. I even tried a few more Quicktime codecs with the same results.
Only H.164 and some png compressed .mov files seem to work. Very frustrating.
I'm surprised thats the case - I am defintley due for an upgrade. Even though this system seems to work ok, struggling a little bit with HD .mov files but yeah, I've been planning a new system for a while.
In QT Pro version 7 (never use QTX!) preferences there should be a check box for legacy codecs. You may need to check it. And it could be in a couple of places; it'll take some looking.
I also see you only have 3 gigs of memory. That's almost nothing in AE terms, and it isn't helping you one bit... especially for HD.