zen cart newbie here...

i'm a web designer. making a site that requires ecommerce and the client wants zen cart. i like using godaddy for hosting and i saw that zen cart is easy to integrate so i said sure!

i am in the preliminary design stages, about to break the site up into working pages. i have questions that i just cannot find the answers to anywhere...

what file type is best to use?
can i use .asp? do i HAVE to use .php?
somebody help!

adding the code to product pages, setting up shopping cart pages
after i have my lovely blank pages, can i just plop the zen cart code into my content div? i must maintain continuity between all pages of the site. i can't have the product and shopping cart pages display in some different looking template.

the client wants to add products herself
she's not familiar with code or web dev. is this possible?

thank you!!!
i'm sure i'll think of more questions.....

leslie