Modify PHP site to include ICal Creation Script

I need some modifications done to a basic script I've purchased called XZero ([login to view URL]). This is a classified ads script however I want to keep the classifieds theme but instead of posting ads create the ability for users to either upload or create .ics calendar files. I need to give users the ability to: #1 upload an .ics file (via the post new ad function --- to be renamed "post new calendar") and #2 create an .ics calendar file and save to their computer so they can upload to the site (one containing multiple events in one file... from the code in the link below). This feature can be done as a separate window or form. So the .ics files will get uploaded or created and stored in the directory and can be searched, sorted, viewed and downloaded by users of the site. The .ics submission form should include title, location, description, source, submitter email. The good news is that much of the calendar-related items I want to do are already figured out here: [login to view URL] They just need to be integrated with the existing XZero script package. Your consideration is appreciated.