I was use it on a shopcart website on asp.
what type of code you need ???
I may post here the code that i was use.
<input type="hidden" name="cmd" value="_ext-enter">
<input type="hidden" name="redirect_cmd" value="_xclick">
<input type="hidden" name="cmd" value="_xclick">
<input type="hidden" name="business" value="email@your.address.com">
<input type="hidden" name="amount" value="<%= formatNumber(intTotal + (intTotal * curTaxRate),2 ) %>">
<input TYPE="hidden" name="shipping" value="<%= formatNumber(curShipRate, 2) %>">
<input type="hidden" name="no_shipping" value="1">
<input type="hidden" name="item_name" value="E-Shop Retail [Order Nº <%=intOrderID%>]">
<input type="hidden" name="item_number" value="<%= strOrderItem %>">
<input type="hidden" name="image_url" value="http://your.address/images/your_logo.gif">
<input type="hidden" name="return" value="http://your.address/your_root/thanks.asp">
<input type="hidden" name="cancel_return" value="http://your.address/your_root/cancel_shopping.asp">
<input type="hidden" name="no_note" value="0">
<input type="hidden" name="undefined_quantity" value="0">
<input type="image" src="http://images.paypal.com/images/x-click-but01.gif" name="submit" alt="Make payments with PayPal - it's fast, free and secure!"></td>
This is the code that i use to can send all data on my checkout to Paypal page, and if you use the somename on the boxes ( as first name, last name, etc.etc. ) you may make that all data that the customer posted on you checkout, transfer to paypal page, and the customer not need again re rewrite the personal data.
But this code is only when you have your own shopcart sistem on your site .. not when you use the shopcart system from paypal.