I have an mpg file that I created.  What is needed so that people can
view it from a web site?

That is, rather than have people download the mpg, is a piece of
software required so I can make a streaming version of the file?

Does it need to be an mpg file?  Windows Media Encoder (search google
for it) is free software that will convert your mpg file into a wmv. 
They could still download the file if they want, but if they clicked
on it normally it would stream (meaning the whole file wouldn't have
to download before they could start watching)

So, when you mean "streaming", what exactly do you mean.  Do you want
something like that where the whole file doesn't have to download
first, or do you want it so that they can't download a copy of the
file?  Do you want to require a specific type of software?

One way to do this would be to use a video editor to convert the file
to .wmv and then embed the video file into the page.

It's what I do on my Paragliding Videos website:

www.marksparaglidingpages.com

Feel free to e-mail me at mandrews1973@gmail.com for assistance (pleased to help)