in win xp pro i am using the scheduled task function to have ccleaner "run" silently and not just "open"at predetermined times.

in ccleaner options the following is recommended presumably to allow the program to open and run automatically.

Command-line parameters:
/AUTO - Runs the cleaner upon loading and then closes the application.

Where and how do you apply the switch?

If you're creating a scheduled task via Windows Scheduled Tasks just create a link to normally run ccleaner.exe. Then edit the program to run so that the parameter looks like this (including the quotes):
"C:\Program Files\CCleaner\ccleaner.exe" /AUTO

You'd use the same parameter if you wanted to create for instance a desktop icon, or All Users startup folder link to automatically and silently run CCleaner.