OK, Nick, back to basics. In Project, the summary by definition, shows the
Duration in working time between the earliest task start and the finish of
the latest task that it summarizes. Nothing more and nothing less. It will
only equal the sum of the Durations of its tasks when each task is scheduled
Finish-to-Start in a chain. The summary's Duration is thus calculated by
Project and cannot be entered.
Whilst Project allows you to assign resources to summaries, you should not
do so if the same resources are assigned to its tasks, as it will be adding
itself to the summarized data giving an erroneous double count.
As for the Gantt splits, Project won't show splits from the Gantt bars it
summarizes. After all, this would be pretty useless if you had lots of
split which overlapped. However, if you have only a few tasks or
non-overlapping tasks, you can select to roll up the Gantt bars to summary
via the Task Information dialogs, which will show the splits.
Hope this helps - please let us know how you get on
Mike Glen
MS Project MVP
See
http://tinyurl.com/2xbhc for Project Tutorials