how to add and initialize a new field in SalesEditLine as parameters

Hi ,

I am just wondering if someone can help me please. I am working on Axapta 3.0 and what i am trying do is when user hits posting > invoice on sales Form , under print options group i want to add another tick box (Noyes enum) Email Invoice so if its tick . where it prints journal i will execute my code . I will appreciate any help .