ASP.NET

NameValueCollection data = new NameValueCollection();
data.Add("cmd", "_cart");
data.Add("business", "test@gmail.com");
data.Add("invoice", 1);

data.Add("item_name_1", "Audi part1");
data.Add("amount_1" , 200);

data.Add("item_name_1", "BMW part1");
data.Add("amount_1" , 300);

data.Add("item_name_2", "carriage");
data.Add("amount_2" , 500);

data.Add("item_name_2" , "insurance");
data.Add("amount_100" , 100);

data.Add("item_name_2", "VAT Amount");
data.Add("amount_2" , 100);                    

data.Add("country", "GB");
data.Add("currency_code", "GBP");
data.Add("cn", "How did you hear about us?");
data.Add("upload", "1");
data.Add("address_override", "1");

data.Add("first_name", "customer first name");
data.Add("last_name", "customer last name");
data.Add("address1", "customer address1");
data.Add("city", "customer city");
data.Add("state", "customer state");
data.Add("zip", "customer post code");

data.Add("return", "http://abc.mysite.net/catalogue/order/PayPalSuccess.aspx");
data.Add("cancel_return", "http://abc.mysite.net/catalogue/order/PayPalFailure.aspx");
data.Add("notify_url", "http://abc.mysite.net/catalogue/order/PayPalNotify.aspx");

HttpHelper.RedirectAndPOST(this.Page, "https://www.paypal.com/cgi-bin/webscr", data);

public static void RedirectAndPOST(Page page, string destinationUrl, NameValueCollection data)
{
    //Prepare the Posting form
    string strForm = PreparePOSTForm(destinationUrl, data);

    //Add a literal control the specified page holding the Post Form, this is to submit the Posting form with the request.
    page.Controls.Add(new LiteralControl(strForm));
}