If you want an effect like the one in the screenshot, then open
pm_messagelist and find this:
Code:
<td><phrase 1="$foldername" 2="$totalmessages" 3="$bbuserinfo[pmtotal]" 4="$permissions[pmquota]">$vbphrase[x_contains_y_z_messages_of_xx]</phrase> (<a href="private.php?do=emptyfolder&folderid=$folderid"><em>$vbphrase[empty_folder]</em></a>)</td>
Then, replace that with:
Code:
<td><phrase 1="$foldername" 2="$totalmessages" 3="$bbuserinfo[pmtotal]" 4="$permissions[pmquota]">$vbphrase[x_contains_y_z_messages_of_xx]</phrase> [<strong>$bbuserinfo[pmpercent]%</strong>] (<a href="private.php?do=emptyfolder&folderid=$folderid"><em>$vbphrase[empty_folder]</em></a>)</td>