This is available in the code as it is. You don't have to modify anything. Just add $totalonline in your template where you want it.
i.e.
Code:
<TR bgcolor="#6c6081" id=cat><TD colspan=6>
<smallfont color="#f5d300"><B>Currently Active Users:</B></smallfont>
<smallfont color="#f5d300"> $activeusers</smallfont><br>
<smallfont>There are currently $totalonline people in the Community. Including $numberregistered members ($numberinvisible invisible) and $numberguest guests.</smallfont></td>
</tr>