If you want to be able to set passwords, just check if you can get some software to lock down your computer. There are some child-safety / parent ... tools you can use for that purpose.
Else, just replace Windows with a GNU/Linux and install Phex locally (though I know that this solution doesn't sound as easy. It's often cheaper and more secure, though
). ->
Kubuntu - The KDE Desktop ,
http://www.knoppix.com/