In the design view of the report, go to View | Sorting and Grouping. Select the field you want to group on, and specify in the properties at the bottom whether you want a header of footer.
In your field footer, you simply add a field that sums a given field in your detail section. Let's say you have a field named "Total" in your detail. In the footer you would put a field with the following control source.
=Sum([Total]) Jim Lunde
compugeeks@hotmail.com
We all agree your theory is crazy, but is it crazy enough?