Apple Final Cut Express HD - Manual (Page 350)

350 Part VI Rough Editing
Example: Editing a Clip Into a Gap in Your Sequence
You can also do the reverse of the previous editing example. Suppose you have a gap
in your edited sequence and you want to fill it with a new clip. You know where you
want the source clip to start, and you don’t particularly care where it ends. You can
specify an In point in the Viewer, and specify In and Out points in the Timeline to
coincide with the gap:
1 Double-click a clip to open it in the Viewer. (This is your source clip.)
2 Specify an In point for the source clip in the Viewer.
3 In the Timeline, move the playhead to the middle of the gap you want to fill.
In point
Move the playhead
into the gap.