Do you mean FFV1, ffvhuff, or something else? ffdshow is the whole encoder/decoder filter, not a specific format.
In any case, you could see if Perian fixes it for you, as it's more-or-less a port of libavcodec to Quicktime (the same way that ffdshow is a port of libavcodec to DirectShow & VFW):
http://www.perian.org/#detailEven if it doesn't enable the particular format those videos are in, it would allow more possibilities - it does list support for HuffYUV and ffvhuff, so you could use the PC to encode in one of those formats and Perian would open them.
Of course, you could also use a new OS X build of mencoder to do the transcoding for use with Perian instead of the PC, as it supports decoding and encoding into those formats too - you'd have to get used to the command-line to get the most use out of it, though. AVIDemux is a more user-friendly option in that regard as well.
http://fixounet.free.fr/avidemux/