If all 6 ads are within one external file, and you wish to show 3 randomly on each column, what you can do is give the first 3 one particular CSS class name, and the other 3, a different one, so something like:
Code:
<div class="groupa">
Content
</div>
<div class="groupa">
Content
</div>
<div class="groupa">
Content
</div>
<div class="groupb">
Content
</div>
<div class="groupb">
Content
</div>
<div class="groupb">
Content
</div>
On the left column, somehow you will have to call:
Code:
<script type="text/javascript">
randomizeContent("groupa")
</script>
And on the right column,
Code:
<script type="text/javascript">
randomizeContent("groupb")
</script>
instead.
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