if the sound is too "low" when playing the movie only and every sound else works ok then it is not a driver problem. usually no driver makes a computer sound louder but it can make it sound better or clearer. do you have an encoded movie or is it from a dvd? if it is an encoded movie then you can strip the audio track re-work it with some audio tools and put it back into the avi or mpg or whatever it is.
hope this helps?
regards, mscrx