[jQuery] “(validate)”

I'm using the jQuery plugin: Validation.

How can I validate, say a textbox inside a specific div element that
has a specific id?

$(document).ready(function() {
$("#aspnetForm").validate({
rules: {
txt_1: {
minlength: 2,
required: true
},
txt_2: {
required: true,
email:true
}
}, messages: {}
});
});

I have a textbox in a div with an id = "testdiv" and the above code
doesn't seem to locate the textbox.

Thanks