michael,
First, it wouldn't do any good to send a Pages document by email, unless the recipient also had a copy of Pages.
Second, Pages files (although they don't look like it in the Finder) are actually packages of files -- the equivalent of a folder full of files. To email a Pages file, select it in the Finder, then ctrl-click on it. Choose Compress (file name) if you have Leopard, or Make Archive of (file name) if you have Tiger. Then email that.
Finally, relating to my first point, if the recipient uses Word, you can choose File > Export in Pages to save a copy in Word or PDF format. If you do that, you don't need to compress it before emailing it.
-Dennis