Are you rendering MPEG-1 or MPEG-2 video? A machine that doesn't have a DirectShow MPEG-2 codec installed will not be able to play MPEG-2 files. MPEG-1 support is built into Windows and doesn't require any additional installations. If you need to create files that are playable on almost any computer, MPEG-1 is the way to go. Most people with Macs can play MPEG-1 also.
I had this experience recently. I had rendered a friend's wedding video
an MPEG-2 file and he wasn't able to play it on his computer. I was
rather disappointed that, even though he has the latest version of
Media Player installed, it wasn't able to automatically find a codec. I
installed SfMPEGWeb.exe on his computer and then the MPEG-2 file
Is there a more generic MPEG-2 codec available for Media Player?
yeah, i agree it's kinda lame to encode to MPEG-2 and not come with playback functions...
but if you go to www.elecard.com you can download a free demo of their MPEG-2 "player" (which is no more than a directshow filter). the demo is unlimited use, but puts a 6x6 white square in the top right corner or something. you can also use WMP to playback MPEG-2 once the elecard codec is installed.