Michael A,
The fill handle in Excel works great for adding a continuous series of items but not so great if you're trying to link non-contiguous cells.
There are several ways to create links in Project. The most labor intensive is to manually enter task IDs into the Predecessor field. You can also select a task's Gantt bar in the middle and drag the mouse down to the task to be linked. Or, you can alternate
select two tasks and use the link icon found under Task > Schedule group. If the tasks to be linked are not both visible, (e.g. task 1 and task 100), you could create a filter that isolates the two tasks and then use one of the above methods. Of course, by
the time you get the filter set up, you could have already entered the link data in the Predecessor field.
If you have a series of tasks you want to link, just select them all and then use thelink icon.
Hope this helps.
John