Here's the link again in case you skipped that last step.
http://mail.google.com/support/bin/answer.py?answer=12336&topic=12911
Which includes attachments and text and header, etc... That's why he
recommended no larger than 14-15 so you don't have to worry about
being close.
AVIs are compressed video, so typically ZIP won't gain you much in the
way of compression.
Thanks.