Custom message when returning from PayPal Standard

Hi,

You can have more than one payment method.

When you are using PayPal Standard the customer leaves the store to go to the paypal site and then returns after payment to the checkoutCompleted.aspx page where a message is diplayed (checkoutCompleted.ascx)

                <%=GetLocaleResourceString("Checkout.YourOrderHasBeenSuccessfullyProcessed")%></b>
            <p>
                <%=GetLocaleResourceString("Checkout.OrderNumber")%>:

These are just standard resource strings.

How do you get to place messages specific to a given payment method and pass information from that payment method?
Particularly when returning from PayPal site

I am using V 1.6

Thanks