wmv has audio with WMP9, but no audio with WMP11

All my wmv videos play fine on my laptop with W2K and WMP9.
But some of my wmv videos have no sound (audio) when played on my new
desktop with Vista and WMP11. The only difference I see in properties is that
the wmv files that play no sound with my WMP11 have an audio bit rate of 48
kbps while those that play normally with audio have an audio bit rate of 80
or 96 kbps.
If I download WMP9 to my desktop, will it run OK under Vista? Will this
solve the problem? Or do I just need part of WMP9 under Vista?
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Roger32909