If a task in one project has a dependency (task dependencies: A relationship between two linked tasks; linked by a dependency between their finish and start dates. There are four kinds of task dependencies: Finish-to-start [FS], Start-to-start [SS], Finish-to-finish [FF], and Start-to-finish [SF].) on a task in another project, you can create a cross-project link between the tasks.
In this demo, I create a cross-project link between tasks in two separate Project 2007 files and then show how the dependency is represented on the Gantt Chart view (Gantt Chart view: A predefined view that displays project tasks on the left side of the view, and graphical bars corresponding to the task's durations on the right side of the view.).