Your set up is a bit different, your DDC site is fully integrated which means the inventory might be difficult to extract and get on Facebook cleanly. You could frame in the entire website like Brent did but it's not a good solution. I bet DDC has some sort of product in the works or already available for Facebook that would accomplish this for you. I'd check in with them before you start fiddling with this work-around.
If you used your inventory as is your code would look like:
<script type="text/javascript" charset="utf-8">
function disp1(var1) {
if (var1=='link_1')
outside_location.setInnerFBML(link_1);
else if (var1=='link_2')
outside_location.setInnerFBML(link_2);
}
</script>
<form>
<select id="gowhere" onchange="disp1(document.getElementById('gowhere').getValue())">
<option>-Select below-
<option value="link_1">View Used Inventory
<option value="link_2">View New Inventory
</select>
</form>
<div id="outside_location"></div>
<fb:js-string var="link_1"><fb:iframe width="760" height="1280" frameborder='0' src='http://www.keenechryslerdodgejeep.com/used-inventory/index.htm?reset=InventoryListing' /></fb:js-string>
<fb:js-string var="link_2"><fb:iframe width="760" height="1280" frameborder='0' src='http://www.keenechryslerdodgejeep.com/new-inventory/index.htm?reset=InventoryListing' /></fb:js-string>
<script type="text/javascript" charset="utf-8">
var outside_location = document.getElementById('outside_location');
</script>
