An interactive purchasing form for my customers.

Hello, I require a form for my website that is interactive and will produce a total for the goods chosen. I seen the exact sort of thing i want on the following website link. [login to view URL] If you select what you require and go to the next page you can see it next lets you choose names and numbers for the shirts chosen and adds to the price if so.. Finally it will take you to checkout. I require this system or if you can point me in the right direction to do this it would be helpful. Regards Chris