To setup accept credit card on your web site you need.
To accept credit cards your web site should support
secure communications with your vistors.
It must suppport SSL encryption and use https protocol
for communication with web browser.
See Web Hosting With SSL
to read about technical aspects of a web site with SSL.
You need to setup your e-commerce software to
communicate with processor company.
Most processors provide you with a library
which can be integrated
to any web platform (asp, php, java, zope, etc.).
This integration is a standard task for any
modern e-commerce software.