To do this, edit the two templates from the section adminhtml. In sales/order/view/items.phtmladding new <col>and <th>for your column. Then sales/order/view/items/renderer/default.phtmladd the appropriate <td>field for this. Use something like this to get the value:
<td><?php print Mage::getModel("catalog/product")->load($_item->getProductId())->getCost(); ?></td>
, !
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