To implement the subject functionality, Enable the Prohibit Browse Group Policy. The policy can target users at User Configuration\Administrative Templates\Windows Components\Task Scheduler or all users of a computer at Computer Configuration\Administrative Templates\Windows Components\Task Scheduler.
The policy is implemented via the Allow Browse value name, a REG_DWORD data type, at HKEY_CURRENT_USER\SOFTWARE\Policies\Microsoft\Windows\Task Scheduler5.0 or KEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\Task Scheduler5.0. A data Value of 1 removes the Browse button from the Scheduled Task wizard and from the Task tab of a tasks Properties. Users can NOT edit the Run line or the Start in line.
NOTE: See the Disable Drag-and-Drop Group Policy.
