Changing PayPal default page

Can you explain what you mean by that? Are you looking at displaying the pay pal page within ur .net win forms application in a web browser control? more details would help

There is a default PayPal's page. From our site we need to pass some parameters to the PayPal page, like site name, amount etc. The GUI which is there is the default PayPal GUI, with user and credit card information fields in the center and user login (using Paypal account) at the right hand side of the page. This page is triggered from say a Checkout page (in the custom web application), i.e., when user clicks on checkout button in checkout page, the paypal page is displayed. This PayPal page now asks either of the two types of information
1.  User details and credit card information
2.  If user already has a paypal account, then the user name and password for that account.

Now what I want is that the second type of information (users paypal login and password) should be displayed in the checkout page only. So the checkout page will ask the user to enter his paypal user name and password (if he already has one). Also, for first type of information which'll still be displayed in the paypal page, I should be able to change the look and feel, like adding few images, changing positioning of textfields etc.
Please let me know if it is possible.