How to validate number of checkbox selected using DynaValidatorForm

[ashish kulkarni]

Hi,
I am using DynaValidatorForm, and i want to validate
number of check boxes selected by the user,
for example to display details, user must select
atleast one checkbox on the the main page before
clicking display details button,
or user must select only one check box for specific
operation..
How do i define this condition in validation.xml??
Ashish