Is there the difference in JS execution in IE6 andIE7

Question

seems thats it is

Answer 1

Short Answer, Yes.

There are subtle nuances and implementation differences. What are the issues you are running into?

Answer 2

Yes, especially in IE8 running in Standards Mode.

e.g.

//in IE6, 7, and IE8 quirks and IE8 compatibility mode, this will return
//the first element with either a 'name' or 'id' attribute value of "description"
//(CasE iNsenSiTIVE)

//in IE8 standards mode, it will return the first element with the
//EXACT id attribute value of "description"
var desc = document.getElementById('description');

plus dozens of changes with .setAttribute() and .getAttribute()