If you want you can show the online/offline-status by hovering over the avatars:
In postbit_avataroffline
replace all with...
Code:
<img src="$avatarurl" border="0" alt="$post[ username] is offline!" style="filter:alpha(opacity=50)">
and in postbit_avatar
replace all with...
Code:
<img src="$avatarurl" border="0" alt="$post[ username] is online!">
Note: delete the empty space between [ and username!