Your problem is probably just XP and ATI's driver. I tried to fix this many times back when I had XP and it's always a dead end. Sometimes XP just doesn't like VMR9, from MPC especially. Have you got '.net2.0' (or maybe 3.0 ) installed? If so you can try the EVR renderer under XP, that might fix the problem. On problem "3" try and block ffdshow from being the first thing MPC asks for decoding x264. First way to do this is to go into ffdshow's video config (from xp start menu).. then under codecs untick x264. If that doesn't work go to "external filters" in MPC then "add filter" and find ffdshow (or any other decoder that does x264.. like Cyberlink PowerDVD) .. press OK and then and select block. Also..... a tip, if you want to use ffdshow for scaling low res video and CoreAVC for x264... which I do... you want to use the external filters option to set CoreAVC to "prefer".. and it'll pop up for the codecs it supports.