Adding to emoticons in Mail

"Bob O." <[email protected]> Mon, 02 Jan 2006 01:38:46 GMT

Newsgroups	gmane.comp.mozilla.devel.macosx
Organization	Road Runner High Speed Online http://www.rr.com
Message-ID	<Gu%[email protected]>

Is it possible to add to the emoticons in the Mail app? Are we stuck 
with what they provide?

Thanks,
Bob O.