var chkbox = document.createElement("INPUT");
chkbox.type = "checkbox";
chkbox.checked=true;
lnk.parentNode.appendChild(chkbox);
The generated Checkbox cannot be correct under IE7. Check the box.
The reason is that the chkbox control has not been initialized (appendChild) before starting to operate its results
Accordingly, change the code to display correctly:
var chkbox = document.createElement("INPUT");
chkbox.type = "checkbox";
lnk.parentNode.appendChild(chkbox);
chkbox.checked=true;