Well you wouldn't. An iMovie project is an xml file that relates to a whole lot of video clips and mkes no sense unless the recipient also has iMovie.
What you seem to want to do is export from iMovie - that is create a movie incorporating your edits and changes - and share that. You do that using the Share menu in iMovie.
However, movies, by their nature a very large files and not really suited for emailing. You might consider uploading it to YouTube, Mobile Me, YouSendIt or a similar service and sending the link to the people you want to see it.