Also everyone should note that if you are running 64 bit windows you need the 64 bit codecs.

http://windows.microsoft.com/en-US/windows7/Codecs-frequently-asked-questions

I personally have only DivX, Nero 10, and PowerDVD (for blu-ray) installed and have never had any problems playing any video file format. I am running Windows 7 x64 Pro.

Reality is but a shadow of one's imagination, is it not?