AC3 Filters problem

I'm using Windows 2000 Pro build 2195, registered AC3filters with the following .cmd:

@echo off
echo Registering AVI-AC3 Filters...
regsvr32 /s iviaudio.ax
regsvr32 /s mpgaudio.ax
echo Finished registering Filters...

but still, when I launch GSPOT to obtain codec information about an XviD movie i got, it says in audio format: ac3 (0x2000) "Dolby Laboratories, Inc" and just below Codec is NOT installed (more info...)

infact when i try to view the movie, i'm not able to hear anything,
the video however is ok.....
what I'm doing wrong?
With VirtualDub in AVI information in the Audio stream section it says:

sampling rate: 48000Hz
channels: 5(Stereo)
sample precision: 0-bit
compression: unknown (tag 2000)
preload skew: 2400 samples (0.50s)
# frames: 163613
Min/avg/max/total frame size: 435/2002/24000 (319897K)
 
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