Here is one way:
First, you'll need a Website Payments Pro merchant account with PayPal. Then, become familiar with the DoDirectPayment API, which will allow you to
process transactions on your site with PayPal working in the background. Customers will be able to fill out their credit card information, etc., on your site without visiting PayPal directly.
This also means that customers will not be required to have a PayPal account in order to make a transaction on your site.
If you proceed this way, you will need SSL certificates, and are required to implement Express Checkout for customers who do not want to make their transaction on your site.
Sample Code to get your feet wet. Good luck!