You will need to clarify / clear your first question.
First, you use the diamond ID many times. Identifiers must be unique and used for a single item. You should use classes, not identifiers, for this.
Secondly, you cannot use href in div tags. You can wrap divs in a tags as follows:
<a href="http://twitter.com/"><div class="diamond"></div></a>
Or, better yet, so that the entire shape is clicked, you can put a inside the div and make the element level element of a equal to 100% width and height:
<div class="diamond"><a href="http://google.com"></a></div>
div a{ width: 100%; height: 100%; display: block; }
JSFiddle example: http://jsfiddle.net/kQj24/1/
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