it is unclear to me if you are expecting to have the flash part interact with another cart, or if you are just trying to replicate the other cart function in flash.
i would not recommend mixing the 2, unless you are quite proficient with php, databases, etc
however if you just want to send data from flash to php, that is done all the time ( at least it used to ....)
a cart often involves updating a databse. discussing that is outside the scope of a flash forum. if you need to do that there are plenty of PHP/MySQL tutorials out there to view.
i am posting a very simple example of a flash to php email form that i created for someone a while back on a different forum. i just tested it and it still works : - )
you can download it, study how it is put toghether and then expand upon it for your own purposes. a working example is always a good place to start!
an html form is created with input elements each with a name and a value. in the same manner, in flash you use a text input, or movieclip with a instance name, and its declared or created value.
( for instance , with a flash text input, the value is usually the text inputted by the user into the filed)
these vars are sent to the php file as URLVariables.
(NOTE: i would be careful of sensitive personal information sent without being further secured )
my bare bones example has 3 input fields ( name, email, message), a dynamic text field for error/success message, and a send button.
hopefully looking this over can help you with your needs