Ok. I'm creating a data which is primarily on Books and the selling of them

The tables are
-Book info
-Author
-Publisher
-Transaction info
-Customer

I'm trying to make a "sales form."

My customer can only purchase 3 books in one purchase and i want to create this form to enable me to store three books being purchased in one go.
How would one go about doing this?
Help would be GREATLY appreciated



I also have a validation problem. In words this is what i want. "This field must include the '@' symbol"

Thanks in advance