Apple Final Cut Pro 5 - Manual (Page 522)

Chapter 11 Finding and Selecting Content in the Timeline 187
II
2 Click the first clip item on any track that you want to include in the selection.
All clip items in all tracks from the point you click onward (either forward or backward)
are selected, as well as any items linked to those items. You can select entire clip items
only; you can’t select a portion of a clip item.
Once you’ve selected a large group of clip items, you can always deselect individual
clip items by Command-clicking them with the Selection tool.
If you click here, all clip
items on all tracks to the
right are selected.
If you click here, all clip
items on all tracks to the
left are selected.