Crystal Reports programming - subreport creation

This is more about programming than about report "design". We really don't need a new report made just it to print sub-reports on demand based on certain criteria. The project must be designed for Crystal Reports version 8.5. This report will print from our POS software and can't be changed or be dependent on the report viewer at all, it must print independently of any input by the user. If conditions are met in the main report we want it to trigger a sub report (or another page) to print on demand only if criteria is met. It must be easy to change the criteria if we decide to later. The field you will be using is mileage. Example: If the contents (or results) of the mileage field is 50,000-75,000 then it will trigger sub-report A to print in addition to the main report. (This will print as a second sheet independent of the header/footer of the main report.) OR If the contents of the mileage field is 75,000-110,000 then it will trigger sub-report B OR If the mileage field is greater than 110,000 then it will trigger sub-report C. We use Crystal Reports publisher to change and edit our own reports currently but don't have the knowledge to do this task. We want to be able to change the looks of the sub-reports or the main report just as easily as we always have so whatever is done it must be easily changed in Publisher. We also need to be able to adjust the criteria if needed (you will have to explain how this is done) such as: print sub-report A if mileage is 45,000-60,000 etc. I have attached a sample report that the sub-reports will have to be generated from so that you can get an idea. NOTE: Not sure if its important or not: I think the POS software "prints" data to a small database or set of tables (Access format) on each computer workstation each time the report is printed. Its my belief that the POS software replaces this database each time the user prints a report, so database the report is generated from only contains information for the current report.