Scheduling WinXP tasks with schtasks.exe and using PHP to execute the command, may sometime fail to work.
This is because, Apache does not have the privilege to access some of the System Files when placing the scheduling. The way I'd do: is by creating a normal user account and assign Apache service to logon as that account.
Open the 'services.msc' in the 'Run' window, look for Apache in the listing, right click and get to 'Properties'. Click at the second tab 'Log On' and fill in the 'This account' fields.
Of course, Apache needs to be installed as Service during its first setup.
Hope this helps anyone.
Fendy Ahmad