//Create your sharelet with desired properties and set button element to false
var object = SHARETHIS.addEntry({
title:'share',
summary: 'Sharing is good for the soul.'},
{button:false});
//Output your customized button
//document.write('<span id="share"><a href="#"><img src="images/b-share.gif" name="Image8" width="20" height="17" border="0"></a></span>');
//document.write('<span id="share"><a href="#" onMouseOut="MM_swapImgRestore()" onMouseOver="MM_swapImage(\'Image8\',\'\',\'images/b-share-o.gif\',1);"><img src="images/b-share.gif" name="Image8" width="20" height="17" border="0"></a></span>');
document.write('<span id="share"><a href="#" onmouseover="move_in(\'Image8\',\'images/icon-tag-h.jpg\'); popUp(event,\'popinfotag\');" onmouseout="move_out(\'Image8\',\'images/icon-tag.jpg\'); popUp(event,\'popinfotag\');"><img src="images/icon-tag.jpg" name="Image8" id="Image8" alt="" width="20" height="17" border="0" /></a></span>');
//Tie customized button to ShareThis button functionality.
var element = document.getElementById("share");
object.attachButton(element);