The simplest way is to use a table. Here is an example using your list information:
<table border="1" cellpadding="2" cellspacing="0" style="border-collapse: collapse" width="450">
<tr>
<td width="7%">Product</td>
<td width="7%" align="center"> </td>
<td width="22%"> </td>
<td width="12%" align="center">Quantity</td>
<td width="13%" align="center">Price</td>
</tr>
<tr>
<td width="7%"><input type="checkbox" value="ON"></td>
<td width="7%" align="center"><img height="30" src="pppImages/Add_Gel_Achiever_Pen.png"></td>
<td width="22%">Add Gel Pen</td>
<td width="12%" align="center"><input type="number" min="1" max="10" size="3"></td>
<td width="13%" align="center">15/-</td>
</tr>
<tr>
<td width="7%"><input type="checkbox" value="ON"></td>
<td width="7%" align="center"><img height="30" src="pppImages/pilot_pen.png"></td>
<td width="22%">Pilot Pen</td>
<td width="12%" align="center"><input type="number" min="1" max="10" size="3"></td>
<td width="13%" align="center">30/-</td>
</tr>
<tr>
<td width="7%"><input type="checkbox" value="ON"></td>
<td width="7%" align="center"><img height="30" src="pppImages/Add_Gel_Achiever_Pen.png"></td>
<td width="22%">Montex Gel Pen</td>
<td width="12%" align="center"><input type="number" min="1" max="10" size="3"></td>
<td width="13%" align="center">15/-</td>
</tr>
</table>
You can put it into your drop down panel and change the widths to your liking.