DATE VALIDATION & CALCULATION ON A FORM

DATE VALIDATION & CALCULATION ON A FORM

Hi,

I have two enquiries...

1) How do you validate one field (Course Finish Date) based on the user input in another (Course Start Date)? I want a message to display "Course Finish Date cannot preceed Course Start Date!"

2) Based on the number of weeks entered (the difference between Course Start Date and Course Finish Date) I want a value to be calculated (in weeks). I also want to use this value to multiply it by the Course Cost Per Week to give a Total Course Cost.


Simple?

Thanks for your help