Finding 2nd and 4th saturdays and sundays in SQL proc or JS

Hi,
  I am not sure about this concept..., pls help me out of this...,
 
I have an entry form with combobox and rad date picker..., I want to do this type of validation...,

if user clicks on Comp-off in combo box and he selects a date for eg 5-1-2013 it should throw the error message "It's not a 2nd or 4th Saturday"

it's possible in SQL proc nor any javascript validation...?

pls give me a quick reply...,

thanks in advance...,