So very much will depend on the Web pages, and the embedded players on those pages. I would contact the Webmaster/designer of the page, to see what the specs. are. It could be that you will need to go with Flash (FLV), WMV, or possibly MP4 (H.264). Also, each Web page might well require different Frame Sizes, and different formats.
Let us know what the pages require, and someone will have some tips for you.
You definitely don't want to put an MPEG on a Web site. They don't stream well.
As Hunt says, Web video is usually WMV (which is most universal), MOV (which is almost as universal and possibly of better quality) and FLV.
The challenge with posting FLV video is that your web page must have a Flash player embedded in it (as YouTube does) or your viewers won't likely be able to watch it.
Personally, I recommend either WMV or MOV at the Cable preset under Share/Personal Computer.