Hi,
If you want to use ALV grid, even using SALV classes, you'd have to do it completely manually, with quite big amount of work.
But from 7.40 there's new, much better way for displaying data (including grouping)
SAP List Viewer with Integrated Data Access (ALV with IDA) - SAP GUI - SAP Library
Quick tutorial:
https://www.youtube.com/watch?v=bLhHciMIzow
At the end of the video you can see an example which does the job you want.
Regards,
Radek