cant get coupons to redeem to my shopping cart

I have some code from paypal that allows me to redeem coupons the problem is when the customer redeems the coupon it takes them to a seperate checkout window. I want them to go to my shopping cart. I have tried everything I can think of to make this work mabey one of you can make it work.

Thanks

Here is the code for the redemption of the coupon

<font color="#0c5a90" size="2" face="Verdana, Arial, Helvetica, sans-serif"><B>Redeem your PayPal Coupon</B></FONT><BR>
<FORM action="http://www.paycodes.com" method="post">
<INPUT type="hidden" name="doredeemcode" value="1">
<font color="#000000" size="2" face="Verdana, Arial, Helvetica, sans-serif"><B>PayCodes™ Coupon: </B></FONT>
<input type="text" name="redeemcode" value="" size="12" maxlength="10"> <input type="image" src="http://www.paycodes.com/gx/redeem.gif" align="middle">
</FORM>

Here is the code for my shopping cart and the item i want to coupon

<Form method="post" action="https://www.paypal.com/cgi-bin/webscr" target="paypal">
<input type="hidden" name="cmd" value="_cart">
<input type="hidden" name="business" value="brett@gardendiscounters.com">
<input type="hidden" name="item_name" value="Deck Table">
<input type="hidden" name="item_number" value="00312">
<input type="hidden" name="amount" value="19.99">
<input type="hidden" name="currency_code" value="USD">
<input type="hidden" name="shipping" value="">
<input type="hidden" name="shipping2" value="">
<input type="hidden" name="handling_cart" value="">
<select name="item_number" size="1">
<option value="Black">Black</option>
<option value="White">White</option>
<option value="EverGreen">Evergreen</option>
</select>
<input type="image" name="add" src="https://www.paypal.com/images/x-click-but22.gif">
</form>