Entourage does not use graphical emoticons (thank goodness!) - but you can
always 'just type them'
You can use the Mac OS X Unicode character palette. System
Preferences/International/Input Menu. Check the "Character Palette" and
Check "Show input menu in the menu bar".
Now, from the input menu (on the right side of the menu bar), choose "Show
Character Palette". You can find the smiley face under View:Roman/by
Category/Miscellaneous or View:Unicode/Unicode Blocks/Miscellaneous Symbols.
You can single click and then click Insert, or double click the icon to have
it be inserted into the current document at the insertion point.
To automate this, you should be able to use AutoCorrect.
Tools/Autocorrect.../Autocorrect and add an entry to replace text as you
type, replacing "

" with "☺". (For those of you who won't see that
character due to lack of character support, it's Unicode's WHITE SMILING
FACE. Theoretically, that should work, though I am having difficulty with
it. ☹