How do you convert idx to some other file?

I downloaded some tv show series,but I can't watch them because they are idx files.I would like to know if there is a possibility to convert them to avi or something like that.I read somewhere that idx means sub but I don't think that's true because I allready have subs for the show.To make long story short,I would like to convert idx to avi or dvd,whatever.Please let me know if that's possible,and keep in mind that I am a computer dummy (big one).Thank you...