envy24HT sound card problems

I have an envy24HT-S sound card with a couple problems I can't solve:

1- I can't install a new driver (V520B). I tried both the install SW
that came with the driver and device manager, each time I get "access
denied." I tried looking for all the related files and setting the
read-only attribute to off without success.

2- There's no sound when video is played (DVD movies, AVI, etc). I
tried both WMP and InterActual Player. However, sound files (mp3, XP
sound files) play fine.

I just installed a new mobo/CPU, but I had the same problems with the
old setup. Thanks.
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Biostar GeForce 6100-M9 939
AMD 4200+ 2.2G X2
EVGA nVidia 7600GT 256MB PCI-e
2 gigs Kingston RAM
450W PSU