This will put the link you need in your footer. It will be visible on the Wedding category page and all galleries within the Wedding category.
Paste this in your footer:
<div id="wedInv">
<p>Do you need Wedding Invitations? Visit <a target="_blank" href="http://www.url Here.com" class="nav">Acme Invitations</a> for the best prices and selection.</p>
</div>
Paste this in your css section:
#wedInv {
display: none;
margin-top: 8px;
text-align: center;}
.category_Weddings #wedInv {display: block;}
Screen grab on how it will look...