From: "dh"

That's a 10 year old hack of Microsoft's WMAv2 codec.
Besides being doubtly legal in most countries, it may
conflict with the modern codec and so it is not a good idea
to install it.

On NT, you just need to create the following registry value:

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows
NT\CurrentVersion\Drivers32]
"msacm.whatever"="c:\x\y\file.acm"

On 9X, you need to create an equivalent entry in system.ini.