Using reg expression

Hi

      i have a reg exp tat will allow to enter only 7 digits, I need to check the values in the txextbox with the reg exp in the onkeypress of the textbox.

reg exp is ^\d{1,7}$   and the textbox is 'TextBox1'  how can i do it. pls help me.

now im using like this but its not working
function TextNum(str)
{var Isvalid=false;
var txtValue = document.getElementById("TextBox1").value;
var reg = /Go to the complete details ...