Large videos show video errors

[Milkymalk]

I reinstalled my WindowsXP a few days ago. Before, everything was fine with playback, but since then, large videos show strange errors and are generally low quality.

Here is a screen (partial):
http://img114.imageshack.us/my.php?image=problemfi9.jpg

It plays fluently, it's only that display error. It also seems to have nothing to do with avc1 encoding because other files with that codec play fine as long as the video size is under 1280x720.

I have a Pentium4 3.8GHz, GeForce6600 with the latest driver from the website, 256MB Video RAM, 1GB RAM.

EDIT: Nevermind... I didn't have DirectX installed yet, which is unusual, but I didn't install any games since I reinstalled Windows. Note for everybody with the same problem: After installing DirectX when VLC is already set up, manually set the video output to Direct3D.