Not sure if you found a solution by now or not, but anyway, I remember that my cousin was looking for this too. Apparently you can either mod the registry or download a third party tool for it, there's no inbuilt option in Vista to do it. He used Vista Manager. It's only a 15 day trial though(I'm certain there's a crack out there), but changes made doesn't disappear when it runs out. There's a bunch of other programs saying they do it as well, but as I don't have Vista this is the only one I know works well.(I take his word for it). Other programs might still be better.
Vista Manager