File transfer FTP HTTP

Thank you in advance to any one who may be able to help. I am looking for a way to have users be able to down load files from a site via FTP and HTTP. This sounds easy enough but here are the details. There will be a application server that users will purchase software form (Under development) The application server will update the database with the item that was purchased. After the purchase is complete the user will be sent to a download server to get the download. The user will have up to 72 hours to get their download. The full pat to the download must be virtual to prevent someone from just putting in the path and doing another download. Ie: ftp://download.thedomain.com/xxx134314x/software.zip The PHP app on the download server will check with the database to confirm what is to be downloaded. Upon a successful download the PHP app will update the database that the download was completed successfully. Thank you, Michael Steinhart PMH Systems mike@opcenter.net