restrict system settings

please help...i want to restrict my computer from changing the system settings. i turned-on the guest account.........success!

but my problem is that, guest account can't connect to the internet. (im using dial-up). the dial-up connection i create from the administrator account, the icon also appears on the desktop of the guest account, but it fails to open in guest account.

please help....is there other way to restrict my computer from accessing the system settings, but using the internet is not restricted....

thanks!