hi ben
afaik h.264 did not start off as a mac or apple thing. It has been used by all sorts of people and i believe the mpeg4 used in bluray video files is also h264…
but whether it will play on your client’s pc really depends on the codecs they have on their computer. Some of my clients cannot even play a basic mpeg-2. Most of these new, efficient codecs require the user to download something, flash, quicktime, wmv, real… but I would agree with David, go with flash, most people have it, erm, flash h264!