There’s a set of free macros – called QuickTrace – at one of my blog entries. That tool sets and applies a filter for predecessors or successors of any selected task, including “driving” or not. It works pretty well, though you have to be comfortable with macros to install and customize it.
Paul’s request is kind of standard for anyone needing to efficiently evaluate logical relationships in a schedule. It’s available as a minor feature of the logic analyzer add-in that I use. I wrote about it in another entry.