Below is how to do it.
1) In your AdminCP > Styles & Templates > Style Manager > Main CSS Options > Additional CSS place the following code:
.postinfo {
border-top: solid 1px #E0E0E0;
border-left: solid 1px #E0E0E0;
border-right: solid 1px #D7D7D7;
border-bottom: solid 1px #D7D7D7;
margin: 3px 5px;
padding: 2px;
color: #808080;
background: #d2dee3;
font-size: 10px;
}
2) You should change the background colour to suit your style. Then click Save.
3) In your AdminCP > Styles & Templates > Style Manager > Edit Templates > postbit_legacy find the following code:
For Join Date: (other Examples At The Bottom!)
<if condition="$post['joindate']"><div>$vbphrase[join_date]: $post[joindate]</div></if>
4) Replace the relevant DIV tags as shown below.
<if condition="$post['joindate']"><div class="postinfo">$vbphrase[join_date]: $post[joindate]</div></if>
5) Replace the revevant DIV tags for any other information you wish to be shown boxed.