Program to time disable Excel spreadsheets

I have an Excel spreadsheet that I want to distribute to other agents. However the quotes are time sensitive and I need to be able to lock agents out after a specific amount of time. I feel that the program should encrypt the spreadsheet, ask the user for a serial number that I would be able to generate, and then start the spreadsheet up if the serial number is valid. I would like a way to go by time and not by date if possible. A small front end would need to be created to ask for a serial number, ask for technical support or visit my web site. I would like to hear your ideas to protect my spreadsheet but still make it usable for my agents. ## Deliverables 1) Complete and fully-functional working program(s) in executable form as well as complete source code of all work done. 2) Installation package that will install the software (in ready-to-run condition) on the platform(s) specified in this bid request. 3) Complete ownership and distribution copyrights to all work purchased. ## Platform Windows 95, 98, 98SE, ME, 2000, XP. ## Deadline information I would like to have the serial generator made in Excel and compatable with Pocket Excel.