MPEG-4 Video codec fix for Windows 9x and NT 4
Sep 12, 1999. By Somebody (http://members.xoom.com/codeczone/codec.htm)

Please note that I take NO RESPONSIBILITY for any problems this fix might 
cause on your system. I have verified it on a local system and on a number 
of other users computers, but there is no way for me to be able to guarantee 
that it will work on each and every system configuration out there.


FIX:
Install the latest (ver 6.4) Microsoft Mediaplayer if you have not already 
done so. Note that this package have an older driver file than what is 
included in the released version of the player/Windows Media Tools. The 
reason for this is that the released driver can have problems with playing 
.avi files encoded with MPEG4. I have not found any problems playing newer 
.asf files with the old driver, but keep in mind that you run on beta software 
if problems should arise. The released version of the MPG4C32.DLL file is also 
available on my webpage.

This installer will replace any existing version of the MPG4C32.DLL file in 
your system directory (system32 on WinNT, Windows 2000). The old file 
(if existing) will be renamed to MPG4C32.BKP by the inf installer.


INSTALLATION INSTRUCTIONS:
To install the package, copy all the files to a temp dir (ie c:\temp) and 
rightclick on the file MPG4INST.INF and select INSTALL from the context menu. 

This will copy the needed file(s) to your system (system32 in WinNT) directory 
and update your system.ini (the registry on WinNT) with the codec/driver 
definitions.

You may have to reboot to make the codec work in your mediaplayer, but it 
_should_ work without a reboot.

You should now be able to play files in mpeg4 v1,2 and 3 format.