To follow up on simbalala's post, if your client's videos are posted as .mpg files, everyone on every platform can view them. If he posts them as .mov files, most people on most platforms can view them. If he posts them as .wmv files, then every Windows user and the Mac users who put themselves to the trouble can view them. If he posts them in Real format, some Mac users and some Windows users who bother to download and install Real Player will view them. He will also alienate a large percentage of his potential audience.