Which control panel? If Flux, this can be done by opening the /themes/default/item/view.php file, finding:
<td><?php echo htmlspecialchars($item->item_id) ?></td>
<?php if ($image=$this->itemImage($item->item_id)): ?>
And adding something along the lines of..
<th>
<img src="/media/item/<?php echo htmlspecialchars($item->item_id) ?>.gif" onerror="ImgError(this);"></th>
.. before that.
And in the top of the file, add:
<script>
function ImgError(source){
source.src = "/media/item/missing.png";
source.onerror = "";
return true;
}</script>
Which will output an image instead of the red X image that displays whenever an item doesn't have an icon. Make a .png image with nothing in it, and save it to the path noted above.
You'll need ALL the icons uploaded to your webhost, though, which are at http://code.google.com/p/fluxcp/downloads/list
I personally will not provide anything further than this, as this should be a good learning experience for you and anyone else looking to do the same. Work it out and let us know how you do!