There seems to be some confusion as to what ffvfw actually is. First of all, this build is outdated. ffvfw is now bundled along with ffdshow (which is MUCH more than an MPEG-4 decoder) and any sane person should just get a recent build of ffdshow if they require ffvfw functionality.

For history's sake, ffvfw was a vfw (Video For Windows) interface for the ffmpeg (or a subset of) ENcoder set. it isn't meant to decode. certain programs expect a VFW interface (VirtualDub for instance) and this allowed the ffmpeg set of encoders to be used with these programs.

Again, if you require this functionality, get ffdshow. Be warned though at the time of this writing the recend builds actually won't allow you to encode xvid or x264 as it was deemed to unstable/moving target. ffshow project is recommending people use standalone xvid or x264 to encode. if you can't be bothered, find a ffdshow that was built circa Feb 2011 or so (i believe, double check for yourself)

Long winded, but there it is.
Enjoy ffdshow, folks!

Installed it and couldnt get it to decode MSMPEG42 so I uninstalled it, while uninstalling it put a file called WININIT.INI in the Windows folder that Spybot says is a piece of Malware called Freshbind. Maybe it was a false alarm but I wont install it again.

Installed and tried to run ffvfw, only problem is that it can't. Everytime i tried to load up it cannot load 'Avi syth', i don't know what this problem is, it could just be because i have winXP i really don't know.

But from the configuration it looks a great program, i wouldn't advise you not to download it, just saying if you have problems your not alone.