all of the parameters sent to world pay are in the hidden form elements on the confirm page:
<form name="checkout_WP_CmpHid" action="https://select.worldpay.com/wcc/purchase" method="post">
<div class="eC_PurchaserInfoWrapper">
<div class="eC_CheckoutFormBody">
</div>
</div>
<table class="eC_ButtonWrapper" border="0" cellpadding="0" cellspacing="0">
<tr>
<td><input type="hidden" name="instId" id="instId" value="dgshsdgh" />
<input type="hidden" name="cartId" id="cartId" value="<?php echo session_id() ?>" />
<input type="hidden" name="amount" id="amount" value="<?php echo $eCart1->GrandTotal() ?>" />
<input type="hidden" name="currency" id="currency" value="USD" />
<input type="hidden" name="desc" id="desc" value="<?php echo $eCart1->TotalColumn("FullDetails") ?>" />
<input type="hidden" name="name" id="name" value="<?php echo((isset($_POST["firstname"]))?$_POST["firstname"]:"") ?> <?php echo((isset($_POST["lastname"]))?$_POST["lastname"]:"") ?>" />
<input type="hidden" name="address" id="address" value="<?php echo((isset($_POST["street1"]))?$_POST["street1"]:"") ?>" />
<input type="hidden" name="postcode" id="postcode" value="<?php echo((isset($_POST["postcode"]))?$_POST["postcode"]:"") ?>" />
<input type="hidden" name="country" id="country" value="<?php echo((isset($_POST["country"]))?$_POST["country"]:"") ?>" />
<input type="hidden" name="tel" id="tel" value="<?php echo((isset($_POST["phone"]))?$_POST["phone"]:"") ?>" />
<input type="hidden" name="fax" id="fax" value="<?php echo((isset($_POST["fax"]))?$_POST["fax"]:"") ?>" />
<input type="hidden" name="email" id="email" value="<?php echo((isset($_POST["email"]))?$_POST["email"]:"") ?>" />
<input type="hidden" name="M_CustomVar1" id="M_CustomVar1" value="<?php echo((isset($_POST["shipping_firstname"]))?$_POST["shipping_firstname"]:"") ?> <?php echo((isset($_POST["shipping_lastname"]))?$_POST["shipping_lastname"]:"") ?>" />
<input type="hidden" name="M_CustomVar2" id="M_CustomVar2" value="<?php echo((isset($_POST["shipping_street1"]))?$_POST["shipping_street1"]:"") ?> <?php echo((isset($_POST["shipping_street2"]))?$_POST["shipping_street2"]:"") ?>" />
<input type="hidden" name="M_CustomVar3" id="M_CustomVar3" value="<?php echo((isset($_POST["shipping_city"]))?$_POST["shipping_city"]:"") ?>" />
<input type="hidden" name="M_CustomVar4" id="M_CustomVar4" value="<?php echo((isset($_POST["shipping_postcode"]))?$_POST["shipping_postcode"]:"") ?>" />
<input type="hidden" name="M_CustomVar5" id="M_CustomVar5" value="<?php echo((isset($_POST["shipping_country"]))?$_POST["shipping_country"]:"") ?>" />
<input type="hidden" name="testMode" id="testMode" value="100" />
<input type="button" value="Modify information" class="eC_FormButton" onclick="history.back();return false;"/><input type="submit" name="Submit_order" id="Submit_order" value="Checkout" class="eC_FormButton" />
</td>
</tr>
</table>
</form>
2) to send the product long description, you would need to add the custom parameter as a hidden element and set the value to the use the log description from the cart, however, you will need to add a loop to loop through the cart to include the long description of all items in the cart.