Greetings:

Do you plan on streaming the video? If so:

MPG simply was not designed for streaming technology. While it is POSSIBLE to stream MPG, it really isn't a viable option.

RealMedia has been losing ground in the market place for years. I wouldn't be investing time into creating media for it.

I would definately go with wmv if you want to stream it.

If you want to make it available for download:

MPG offers better quality, although it's compression isn't as impressive as that of wmv or RealMedia. It's a good solution if you want to make higher quality media available for download.

I'm sure that members of "The Cult of The Macintosh" will start preaching Quick Time in this thread soon. Ignore them, their path is a sinful one......