thank you for your answer

A couple of people I know have had similar problems..

I've found installing the Nimo Codec pack (a collection of video and audio codecs) usually resolves this .. generally the default options should do you .. if you install all of them you can crash media player :P (but easily fixed by uninstalling)

try here: http://www.btinternet.com/~nimosiro/

At times when I download certain audio, .avi file from kazaa, the video plays fine but i cannot hear any audio. On doing a search on the net I could find quiet a few softwares ( I use vidtrace) which tell me the video codec that is required, but I am not able to get the audio codecs used to encode the same.