Vista's parental controls are a joke. They are very weak and very
limited in what they can do, but then I guess you shouldn't expect
much for free.
If you're serious about parental controls spend a few bucks and buy a
good third party parental control. I use a program called PC Chaperone
(
http://www.pc-chaperone.com). It is easy to use and has more features
then you will ever need, in fact more then any other program I've
tested. In a side-by-side comparison it blows the Vista parental
controls away.