I would go with jQuery or some other Javascript Framework, the selectors just rock and NOT class XY is rather easy to achieve.
As Pekka pointed out I am not sure what brothers you want to target. getElementsByClassName() is implemented by almost all browsers (you know which one doesn't work, don't you?).
I found a rather nifty solution on devshed to also make it work in IE:
onload=function(){
if (document.getElementsByClassName == undefined) {
document.getElementsByClassName = function(className)
{
var hasClassName = new RegExp("(?:^|\\s)" + className + "(?:$|\\s)");
var allElements = document.getElementsByTagName("*");
var results = [];
var element;
for (var i = 0; (element = allElements[i]) != null; i++) {
var elementClass = element.className;
if (elementClass && elementClass.indexOf(className) != -1 && hasClassName.test(elementClass))
results.push(element);
}
return results;
}
}
}
All you need to do now is to iterate through all your div classes and negate the one you DON'T want.