I'd like help summing a field on a report, I don't need a 'running sum.' I have the data grouped on the report according to (x). I'd like to sum each X individually (at the end of every grouped detail section), and then sum all X's collectively, at the end of the report.

In the group footer put a field with a control source of:
=Sum(YourField)
Copy the control and place it in the report footer also.