I didn't see a property for limiting the number of items displayed in a group. If there are most than N items I would want a scrollbar to display. Is this possible?
You did not mention which style you were using, but none of the styles show a scrollbar for items. The styles that support expansion (ExplorerBar, VSToolbox) make the group as large as it needs to be to display all items. The styles that support selection (Listbar, Toolbox, OutlookNavigationPane) display a scroll button when the items can't all fit in the amount of space available to the control.