the easiest way is to be the administrator of the computer then control the usage of other users (guest accounts). to do that, log in as administrator, then click
Start > Run > Type : "Control UserPasswords2"
highlight the administrator account and click Property. on the setting, prohibit the download, run and installation of any programs and software in your PC. don't forget to password protect your administrator's account then restart the computer after making the changes. this time, guest users cannot be able to download, run and install any programs/softwares in your PC.