Validation Of Dynamically Created Text Boxes

I'm using ASP 3.0,IIS and Java script.I have created some text boxes Dynamically using java script.So the text boxes has got the same name. This is the code i'm using for that..

aTable1=document.all('myTableTBody1')
aRow1 = aTable1.insertRow(aTable1.rows.length);
aRow =aRow1
aCell = aRow.insertCell(0);
aCell.align = "Left";
aCell.width = "5%";
aCell.innerHTML = "<input type='text' name='Course' size='20'>";

Problem is that when i'm doing client side validation using javascript its not taking values..Here 2 or 3 or 4 text boxes with the course will be created when i use
this code:

if (document.Qualificationdetails.Course.value == "") {
window.alert ("Enter Course !");
document.Qualificationdetails.Course.focus();
return false;
}

it does not give any validation...