Congratulations, you win today's "least informative thread title!"
Ah, but the day is still young ...
So you want to send a video by email, eh? My first question would be "how long is it" (the video I mean). Because if it's more than a minute or so, forget it - only your most top-tier high-speed friends are going to appreciate this. The rest will block you and curse your name for having spammed or filled up their measly inboxes, and make them wait while your magnum opus loads so painfully slowly (assuming they're lucky enough to have the codecs to see it at all after all that).
If it IS very short as described above, you'll need to both change the format AND the resolution to send it via email. iMovie (included on your Mac) can do all this for you. Just choose "Email" from the Share menu and that should take care of it.
If we're talking about something longer than a minute, you'd be better advised to post it to a hosted web page somewhere and simply email the URL to people. That way, they won't hate you.
Again, iMovie (included) can do this for you. Choose "Share" and pick either a MobileMe Gallery (if you don't have an MM account, now might be a good moment to give the 60-day free trial a spin), or YouTube (you don't have to make the video public, you can password it). You'll need a (free) YouTube/Google account, of course.