To Show an user with presence indicator on a webpart

<span>
 <img width="12" src="/_layouts/images/blank.gif" onload="IMNRC('[USERMAIL]')" id="IMID[GUID]" ShowOfflinePawn=1 alt="Presence bubble">[USERNAME]</span>

http://stackoverflow.com/questions/637915/adding-presence-indicator-to-a-custom-web-part