1) Using your WowBB administrator login, go to the admin panel and click on the Themes link

2) Scroll down until you find the Edit: dropdown menu, and select Templates:

3) Scroll down, and click on the index_who_is_online link:

4) Add the following content at the end of the template contents:

!table_header($table_width='98%', $table_title='Flashchat Users')
<TABLE WIDTH="100%" CELLPADDING="5" CELLSPACING="0" BORDER="0">
<TR>
<TD>
<iframe frameborder="0" src="chat/info_embedded.php" style="width: 100%; margin: 0; padding: 0; border: 0; overflow: hidden;" scrolling="no" border="0" allowtransparency="true"></iframe>
</TD>
</TR>
</TABLE>
!table_footer

You can add a height="<height_in_pixels>" parameter to the <iframe> tag to adjust the height of the userlist.

5) Click on the Save button

You'll see something like this at the bottom of your home page: