you could also do this, which would put the display name in the place of a username
create a new custom porfile feild named display name, make it hidden - required - and you have to fill it in
now go to ACP > Templated > Modify > Extend > Postbit templates > Postbit
now replace
Code:
<normalfont><b>$post[username]</b></normalfont><br>
with
Code:
<normalfont><!-- <b>$post[username]</b></normalfont><br> --><b>$userinfo[field7]</b><br>
and replace 7 with your custom profile feild number
just take out the <!-- --> if you want both to be displayed and change
Code:
<b>$userinfo[field7]</b><br>
with
Code:
<i>$userinfo[field7]</i><br>