Writing a PHP Web application

Hello, What are the options to get code to run on the server (every XX minutes), without any user interaction, etc. Example 1: If I have a directory that contains files, can I write a script that will delete all files older that 5 days? Example 2: If I write an email web application, and the user wants to send an email to 50 people, can I write a script that will send emails individually XX seconds apart from each other, but have the progress interfaced with the web page the user is on so they can see the percentage progress of sent emails. Is this possible? How do I do such things? Are there any resources available that can help me with this? Also, back to the email example, is it possible that once an email is composed and sent, that the web application can scan the email for viruses, then show a message to the user if a virus was found in their email, if no virus found, the email is then sent to the users as above. How would I scan an email for viruses (or spam?)? And, scan it only once so that system resources are not used to scan unnecessarily for every recipient? Any help would be greatly appreciated. Thanks Tim