The link NeedKarma sent you is a great guide and will help you understand what you need to do. The gist of the answer really is to "resize" your photos before you send them via email. The article didn't exactly tell you how to do that but it hinted that you can do it with any number of programs.
A great free tool to use to manage pictures (and resize them) is
Picasa which is offered for free from Google (
Picasa) I have used it and I found that it was a very nice tool especially for a beginner.
Casey