First off, I'll echo what VanguardLH has already pointed out. You're looking for
a technological answer to what is essentially a parenting issue. The unfortunate
fact is that no matter what simple steps you take to control his computer usage,
your son will probably find a way around it.
Here's a second vote for placing the computer in a locked room with a case lock
installed. A BIOS password should also be configured. Consult the documentation
for your system to see how this is accomplished. There are bootable CDs easily
available on the internet that your son can use to get around your efforts. You
need to prevent him from configuring the computer to boot from a CD. As has
already been pointed out, the computer should be booting from the hard drive
first.
As for how your son is promoting his account to administrative status, the first
thing that comes to mind is that he's logging on with the built-in Administrator
account. Every computer with XP installed has an account named Administrator
that is not initially password protected.
In the case of XP Media Center Edition, as soon as you create a second
administrative level account, the Administrator account goes into hiding. In
order to log on to this account, log off from your account. This should bring
you to the Welcome screen. At the Welcome screen, hit the Ctrl + Alt + Delete
keys at the same time twice. Enter Administrator in the User Name box. Leave the
Password box blank. If you can log on with the Administrator account, set up a
password and log off.
If you are told that the password is wrong, log back on to Windows with your
user account. Go to Start -> Run and enter the following command in the open
box.
control userpasswords2
On the User page, click on Administrator in the "Users for this computer" box.
In the Password for Administrator box, hit the Reset Password button. Enter the
password you want for this account. Close all open windows, log off from your
account, and attempt to log on as Administrator using the procedure outlined
earlier.
Once you've protected the Administrator account with a password only you know,
demote your son's account to limited status.
You might want to take a look at this free program from Microsoft.
Windows SteadyState
http://www.microsoft.com/windows/products/winfamily/sharedaccess/default.mspx
Good luck
Nepatsfan