how to run 'periodic'

Hi. I have written a script which outputs a rather large ZIP file ( 200 MB ) by collecting a large amount of PDF files and html pages. When the script is done, the available amount of free memory has decreased by about 20 - 30%. Running 'periodic' on my machine ( Apple Xserve G5 with Mac OS 10.4 server) restores the available memory to a more proper size. The question is: how can I execute 'periodic daily|weekly|monthly' from my script? Is this possible at all? I know that 'periodic' needs root. And all PHP code is executed as www user which doesn't have root privileges. Would I compromise my servers security when granting root privileges to a script that executes 'periodic' (which could be called from the script that outputs the ZIP archive)? thanks /frank