ok so you need two profile fields.
Lets imagine that they are set like this
field5 = Zip Code
field6 = show zip code (Yes No options)
what you would need to use is this.
Code:
<if condition="$post[field6]=='Yes'"><div class="smallfont">Zip Code: $post[field5]</div></if>
put it somewhere around your posts bit in your postbit template.
look for something like
Code:
<div>
$vbphrase[posts]: $post[posts]
</div>
Just change the 5 and 6 to fit your field numbers.
Also, this is assuming that the option to show/hide is radio buttons and the text are Yes and No.