Assume:

$ = document.getElementById;
pre = $('pre-text-element');  //pre-text-element is the ID of my pre tag element

You cannot use:

$('element').innerHTML = 'line1\nline2'; //will not work in IE7

You must do this:

e = $('element');
while(kid=e.firstChild) { e.removeChild(kid) }  //remove all