[Dan.roh]

In skin1/main/product_details.tpl the code that was added to create the extra field in your "Add new product" is as follows. You would need to add it where you want your extra field to appear

{/if}

<tr>
    {if $geid ne ''}<td width="15" class="TableSubHead"><input type="checkbox" value="Y" name="fields[stock_indicator]" /></td>{/if}
    <td class="FormButton" nowrap="nowrap">{$lng.lbl_stock_indicator}</td>
    <td class="ProductDetails">
    <input type="text" name="stock_indicator" size="2" value="{$product.stock_indicator}" />
    </td>
</tr>

In skin1/customer/main/product.tpl this code was added

<tr>
    <td>Availabilty:</td>
    <td>
        {if $product.stock_indicator ge 1}
            <span style="color: green; font-size: 12px; font-weight: bold;">{$lng.lbl_product_in_stock_now|regex_replace:"/<br[^>]*>/iS":" "}</span>
        {else}
            <span style="color: orange; font-size: 12px; font-weight: bold;">{$lng.lbl_product_out_of_stock|regex_replace:"/<br[^>]*>/iS":" "}</span>
        {/if}
    </td>
</tr>

In skin1/customer/mainproducts.tpl this was added

{if $products[product].stock_indicator ge 1}                        
                        <span style="color: green; font-size: 12px; font-weight: bold;">{$lng.lbl_product_in_stock_now}</span>                        
                        {else}                        
                        <span style="color: orange; font-size: 12px; font-weight: bold;">{$lng.lbl_product_out_of_stock}</span>                        
                        {/if}                    
                    </td>  

Don't ask me where to place the code as mine would be different from yours as our products layout is different. You would also need to create lanuage variables