Hi Michael,
First of all I am not clear what you are trying to do. You want to inset a summary based on a group which you have created ? If so, right click on the numeric field which is there in report detail section and go in Insert --Summary-- It will display a window where you can click on a drop down which is there in Summary location and select your group name or you may click in check box 'Add to All Group Levels'
This will insert summary.
Thanks,
Sastry