Adding PayPal Checkout to my 3rd-party Shopping Cart

What I need to do and have not been able to figure out is Add Paypal check out to my web site installed shopping cart. I want to use my own shopping cart that was pre installed With form for checking buyers shipping information if they choose to mail there payment rather than checkout Via paypal. But somewhere one the same page I would like the choice to check out Via paypal. when they choose paypal as there choice i would like them to be redirected to a new page for the checkout with there items they have put in the shopping chart [login to view URL] all that makes sense. ## Deliverables 1) Complete and fully-functional working program(s) in executable form as well as complete source code of all work done. 2) Installation package that will install the software (in ready-to-run condition) on the platform(s) specified in this bid request. 3) Exclusive and complete copyrights to all work purchased. (No GPL, GNU, 3rd party components, etc. unless all copyright ramifications are explained AND AGREED TO by the buyer on the site per the coder's Seller Legal Agreement). ## Platform i am guessing that you would need the same as i have which is windows xp not sure if that will matter for my odjective here