Let me start off by saying I wish there was a cleaner way to do this like using an array of searches and replaces much like in PHP, but unfortunately I couldn't find one. Secondly this script isn't exactly what you wanted, although it does replace smileys with nothing, it is intended for you to fill out the new urls for each smiley and then it'll replace them. Otherwise I could of made a much shorter smiley to remove it all. Anyway, here it is enjoy.
Code:
// ==UserScript==
// @name Bebo Smilies
// @namespace http://www.mrcraig.net
// @description Converts bebo smilies into more visually appealing ones.
// @include http://www.bebo.com/*
// ==/UserScript==
var comments = document.getElementById('content_Comment').innerHTML;
/* The Original Smileys */
var comments = comments.replace(/<img.*src="http:\/\/s.bebo.com\/img\/smiley.gif"[^>]*>/g, ''); // Happy Smiley
var comments = comments.replace(/<img.*src="http:\/\/s.bebo.com\/img\/smiley_sad.gif"[^>]*>/g, ''); // Sad Smiley
var comments = comments.replace(/<img.*src="http:\/\/s.bebo.com\/img\/smiley_big_grin.gif"[^>]*>/g, ''); // Grinning Smiley
var comments = comments.replace(/<img.*src="http:\/\/s.bebo.com\/img\/smiley_oh.gif"[^>]*>/g, ''); // Oh Smiley
var comments = comments.replace(/<img.*src="http:\/\/s.bebo.com\/img\/smiley_ohmygod.gif"[^>]*>/g, ''); // Oh My God Smiley
var comments = comments.replace(/<img.*src="http:\/\/s.bebo.com\/img\/smiley_laugh.gif"[^>]*>/g, ''); // Laughing Smiley
var comments = comments.replace(/<img.*src="http:\/\/s.bebo.com\/img\/smiley_wink.gif"[^>]*>/g, ''); // Winking Smiley
var comments = comments.replace(/<img.*src="http:\/\/s.bebo.com\/img\/smiley_grrr.gif"[^>]*>/g, ''); // Angry Smiley
var comments = comments.replace(/<img.*src="http:\/\/s.bebo.com\/img\/smiley_sleep.gif"[^>]*>/g, ''); // Sleepy Smiley
var comments = comments.replace(/<img.*src="http:\/\/s.bebo.com\/img\/smiley_toungeout.gif"[^>]*>/g, ''); // Tounge Out Smiley
/* The Extra Smileys */
var comments = comments.replace(/<img.*src="http:\/\/s.bebo.com\/img\/smiley\/bebosummer.gif"[^>]*>/g, ''); // Bebo Summer
var comments = comments.replace(/<img.*src="http:\/\/s.bebo.com\/img\/smiley\/gold.gif"[^>]*>/g, ''); // Gold Medal
var comments = comments.replace(/<img.*src="http:\/\/s.bebo.com\/img\/smiley\/silver.gif"[^>]*>/g, ''); // Silver Medal
var comments = comments.replace(/<img.*src="http:\/\/s.bebo.com\/img\/smiley\/bronze.gif"[^>]*>/g, ''); // Bronze Medal
var comments = comments.replace(/<img.*src="http:\/\/s.bebo.com\/img\/mobile\/mobileB.gif"[^>]*>/g, ''); // Mobile Bebo
var comments = comments.replace(/<img.*src="http:\/\/s.bebo.com\/img\/smiley\/skittles-green.gif"[^>]*>/g, ''); // Skittle (Green)
var comments = comments.replace(/<img.*src="http:\/\/s.bebo.com\/img\/smiley\/skittles-yellow.gif"[^>]*>/g, ''); // Skittle (Yellow)
var comments = comments.replace(/<img.*src="http:\/\/s.bebo.com\/img\/smiley\/skittles-orange.gif"[^>]*>/g, ''); // Skittle (Orange)
var comments = comments.replace(/<img.*src="http:\/\/s.bebo.com\/img\/smiley\/skittles-pink.gif"[^>]*>/g, ''); // Skittle (Pink)
var comments = comments.replace(/<img.*src="http:\/\/s.bebo.com\/img\/smiley\/skittles-red.gif"[^>]*>/g, ''); // Skittle (Red)
var comments = comments.replace(/<img.*src="http:\/\/s.bebo.com\/img\/smiley\/skittles-purple.gif"[^>]*>/g, ''); // Skittle (Purple)
var comments = comments.replace(/<img.*src="http:\/\/s.bebo.com\/img\/smiley\/4leafclover.gif"[^>]*>/g, ''); // Four Leaf Clover
var comments = comments.replace(/<img.*src="http:\/\/s.bebo.com\/img\/smiley_bebo.gif"[^>]*>/g, ''); // Bebo
var comments = comments.replace(/<img.*src="http:\/\/s.bebo.com\/img\/smiley\/rednose.gif"[^>]*>/g, ''); // Red Nose
var comments = comments.replace(/<img.*src="http:\/\/s.bebo.com\/img\/smiley\/jack-o-lantern.gif"[^>]*>/g, ''); // Jack-O-Lantern
var comments = comments.replace(/<img.*src="http:\/\/s.bebo.com\/img\/smiley\/cupid.gif"[^>]*>/g, ''); // Cupid
var comments = comments.replace(/<img.*src="http:\/\/s.bebo.com\/img\/smiley_moon.gif"[^>]*>/g, ''); // Smiley Mooning
document.getElementById('content_Comment').innerHTML = comments;