How do I change images with a dropdown menu?

Here’s a portion of my html. I’m using a google checkout form and I have a dropdown menu with 3 options. When someone uses the dropdown menu I want the “product” image to change depending on what they select in the dropdown menu – currently the default image is [b]Nux_buy_1.jpg[/b], but I also have [b]Nux_buy_5.jpg[/b] and [b]Nux_buy_24.jpg[/b].

[code]<td class=”style8″><p align=”center”><img src=”images/Nux_buy_1.jpg” width=”350″ height=”280″ id=”product” /><br />
</p>
<form action=”https://checkout.google.com/api/checkout/v2/checkoutForm/Merchant/430266264734591″ id=”BB_BuyButtonForm” method=”post” name=”BB_BuyButtonForm”>
<div align=”center”>
<table cellpadding=”5″ cellspacing=”0″ width=”1%”>
<tr>
<td align=”right” width=”1%”><select name=”item_selection_1″>
<option value=”1″>$4.99 – 1 Bottle (4 doses)</option>
<option value=”2″>$19.99 – 5 Bottles (Party Pack)</option>
<option value=”3″>$74.99 – 24 Bottles (Case)</option>
</select>
<input name=”item_option_name_1″ type=”hidden” value=”1 Bottle (4 doses)”/>
<input name=”item_option_price_1″ type=”hidden” value=”4.99″/>
<input name=”item_option_description_1″ type=”hidden” value=””/>
<input name=”item_option_quantity_1″ type=”hidden” value=”1″/>
<input name=”item_option_currency_1″ type=”hidden” value=”USD”/>
<input name=”item_option_name_2″ type=”hidden” value=”5 Bottles (Party Pack)”/>
<input name=”item_option_price_2″ type=”hidden” value=”19.99″/>
<input name=”item_option_description_2″ type=”hidden” value=””/>
<input name=”item_option_quantity_2″ type=”hidden” value=”1″/>
<input name=”item_option_currency_2″ type=”hidden” value=”USD”/>
<input name=”item_option_name_3″ type=”hidden” value=”24 Bottles (Case)”/>
<input name=”item_option_price_3″ type=”hidden” value=”74.99″/>
<input name=”item_option_description_3″ type=”hidden” value=””/>
<input name=”item_option_quantity_3″ type=”hidden” value=”1″/>
<input name=”item_option_currency_3″ type=”hidden” value=”USD”/> </td>
<td align=”left” width=”1%”><input alt=”” src=”https://checkout.google.com/buttons/buy.gif?merchant_id=430266264734591&amp;w=121&amp;h=44&amp;style=white&amp;variant=text&amp;loc=en_US” type=”image”/> [/code]

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