If you have three checkboxes (cb1, cb2, and cb3) the following script on the cb1 change event will set cb2 and cb3, where '1' is the default 'On' value.
form1.subform1.cb1::change - (JavaScript, client)
if (cb1.rawValue == "1") {
cb2.rawValue = "1";
cb3.rawValue = "1";
}
else {
cb2.rawValue = "0";
cb3.rawValue = "0";
}
Steve