I'm currently building a webpage with javascript with numerous computer parts where a customer can choose parts to suit thier needs for a computer system. I have it set up so they click a check box in each category e.g processors, memory etc which then adds up a total price. I dont have a problem getting prices to add up when the checkboxes are checked but i need an error checking script so that they can only choose 1 item in a category for example they can only choose 1 processor and if they try to choose 2 processors i want it so that it spits out an error message like "You can only choose 1 processor". Any suggestions would be greatly appreciated.