What are the options to get code to run on the server (every XX minutes), without any user interaction, etc.
If you are running on a unix like system (linux, freebsd, solaris, etc.) cron can do this for you. See this: http://en.wikipedia.org/wiki/Cron
If on windows there are probably scheduling applications, but I don't know anything about them.
Example 1: If I have a directory that contains files, can I write a script that will delete all files older that 5 days?
Yes. Write the script to do what you want it to do and then have cron execute it on the time period you define.
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.
Yes. This is a bit trickier as you would need to coordinate with a backend process that looks for emails that are ready to send them, does the sending and also writes out some status info (either to a temp file or to a database, or to shared memory). Then your web page would need to repeatedly check that status to update the user on the progress.
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.
Yes. You could install a virus scanner such as ClamAV (http://www.clamav.net/) and have it scan the message prior to handing it off to the backend process that does the sending.
How would I scan an email for viruses (or spam?)?
Same idea, but use something like SpamAssassin (http://spamassassin.apache.org/)
And, scan it only once so that system resources are not used to scan unnecessarily for every recipient?
Sure. Just do it before handing it off to the script that actually does the mailing...
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