Prueba esto:
Código PHP:
<HTML>
<HEAD><title>partes de pc's exclusivas 2011</title></HEAD>
<center><p><font size="36" font color="red"> BYNGUI PARTES</font><br></p></center>
<BODY BACKGROUND="claymore-wallpaper-04.gif">
<br><br>
<br><br>
<center>
<table width="600" border="0" cellspacing="2" cellpadding="1">
<tr><td></td>
<td width="192"><div align="right"><font color="White">NOMBRE:</font></div></td>
<td align="left"><input name="nombre" type="text" size="30" tabindex="7" style="background-color: #CCCCCC; color: #000000; border: 0 "></td>
</tr>
<tr><td></td>
<td width="192"><div align="right"><font color="White">Direccion:</font></div></td>
<td align="left"><input name="direccion" type="text" size="50" tabindex="7" style="background-color: #CCCCCC; color: #000000; border: 0 "></td>
</tr>
<tr><td></td>
<td width="192"><div align="right"><font color="White">Cidudad</font></div></td>
<td align="left"><input name="ciudad" type="text" size="30" tabindex="9" style="background-color: #CCCCCC; color: #000000; border: 3 "></td>
</tr>
<tr><td></td>
<td width="192"><div align="right"><font color="White">Telefono :</font></div></td>
<td align="left"><input name="telefono" type="text" size="25" tabindex="9" style="background-color: #CCCCCC; color: #000000; border: 3 "></td>
</tr>
<tr><td></td>
<td width="192"><div align="right"><font color="White">Correo
electronico:</font></div></td>
<td align="left"><input name="correo" type="text" id="email" size="34" tabindex="10" style="background-color: #CCCCCC; color: #000000; border: 3 "></td>
</tr>
<tr><td></td>
<td width="192"><div align="right"><font color="White">fecha
:</font></div></td>
<td align="left"><input name="fecha" type="text" id="email" size="12" tabindex="10" style="background-color: #CCCCCC; color: #000000; border: 3 "></td>
</tr>
<tr><td></td>
<td width="192"><div align="right"><font color="White">Nº
factura :</font></div></td>
<td align="left"><input name="factura" type="text" id="factura" size="10" tabindex="10" style="background-color: #CCCCCC; color: #000000; border: 3 "></td>
</tr>
</table>
<br>
<br>
<form action="<?php echo $_SERVER['PHP_SELF']; ?>"method="post">
<table align=center border=4 cellpadding=5 cellspacing=6 >
<tr>
<td colspan=2 align=center><font color="White">Seleccione TORRE : </font></td>
<td colspan=2 align=center>
<select name="op1">
<option value="1" >thlelemarker</option>
<option value="2">Mustiff ATX</option>
<option value="3">coller marter 900w</option>
<option value="4">delux de lujo </option>
</select>
</td>
</tr>
<tr>
<td colspan=2 align=center><font color="White">Seleccione tipo de Disco Duro : </font></td>
<td colspan=2 align=center>
<select name="op2">
<option value="1">SATA Hitachi 160GB</option>
<option value="2">SATA Hitachi 300GB</option>
<option value="3">SATA Maxtor 500GB</option>
<option value="4">SATA segeate 1TB</option>
</select>
</td>
</tr>
<tr>
<td colspan=2 align=center><font color="White">Seleccione tipo de Memoria : </font></td>
<td colspan=2 align=center>
<select name="op3">
<option value="1">DDR2 256MB </option>
<option value="2">DDR2 512MB </option>
<option value="3">DDR2 1GB </option>
<option value="4">DDR3 1GB </option>
<option vauue="5">DDR3 2GB </option>
<option value="6">DDR3 4GB </option>
</select>
</td>
</tr>
<tr>
<td colspan=2 align=center><font color="White">Seleccione tipo de Placabase : </font></td>
<td colspan=2 align=center>
<select name="op4">
<option value="1">MBRD Asus eco m785 am3 </option>
<option value"2">MBRD Intel lg1165 </option>
<option value="3">MBRD msi am3 </option>
<option value="4">MBRD asus corsair 5 am3 </option>
<option value="5">MBRD inte corei7 pegout </option>
</select>
</td>
</tr>
<tr>
<td colspan=2 align=center><font color="White">Seleccione tipo de Monitor: </font></td>
<td colspan=2 align=center>
<select name="op5">
<option value="1">Samsung 23 LCD</option>
<option value="2">Sony 20 LCD</option>
<option value="3">Dell 17 LED</option>
<option value="4">LG 24 LED</option>
</select>
</td>
</tr>
<tr>
<TD colspan=4 ALIGN=CENTER><input type="submit" value="Cotizar">
</TD>
</tr>
</table>
</form>
</center>
<br><br>
</BODY>
</HTML>
<?
$op1 = $_POST["op1"];
$op1torre = array("1" => 500000, "2" => 250000, "3" => 125000, "4" => 5000);
$op2 = $_POST["op2"];
$op2disco = array("1" => 700000, "2" => 594000, "3" => 240000, "4" => 340000);
$op3 = $_POST["op3"];
$op3memoria = array("1" => 120000, "2" => 220000, "3" => 124000, "4" => 156000, "5" => 340000, "6" => 450000);
$op4 = $_POST["op4"];
$op4board = array("1" => 120000, "2" => 220000, "3" => 124000, "4" => 156000, "5" => 45000);
$op5 = $_POST["op5"];
$op5lcd = array("1" => 340000, "2" => 5000000, "3" => 340000, "4" => 350000);
$total = $op1torre[$op1] + $op2disco[$op2] + $op3memoria[$op3] + $op4board[$op4] + $op5lcd[$op5];
echo "<center><table width=690 border=2><tr><td width=500>la torre cuesta: </td><td>$" . $op1torre[$op1] . "</td></tr>
<tr><td width=500>el disco duro cuesta: </td><td>$" . $op2disco[$op2] . "</td></tr>
<tr><td width=500>la memoria ram cuesta </td><td>$" . $op3memoria[$op3] . "</td></tr>
<tr><td width=500>la board cuesta </td><td>$" . $op4board[$op4] . "</td></tr>
<tr><td width=500>el monitor cuesta </td><td>$" . $op5lcd[$op5] . "</td></tr>
<tr><td width=500>el total de la compra es </td><td>$" . $total . "</td></tr></table></center>";
?>