Profile info in thread display.

[MediaHound]

Assuming 99% of the time where you will be adding this, you will break it to a new line, so...
Adding the break after the if instead of before the if is helpful so you don't get a blank line if the users did not fill in the profile field.

<if condition="$post[fieldX]"><br>First Name: $post[fieldX]</if>

added:
Using a div instead of a break should give you the same effect, you can do that like this:

<if condition="$post[fieldX]"><div>First Name: $post[fieldX]</div></if>