There's been some discussion on these forums about using add-ins to adapt Outlook tasks to manage GTD Projects and Next Actions. I tried the Netcentrics add-in and experimented with other approaches. I found that most of my projects involved one or more email threads and associating those messages with tasks was awkward. I decided to try managing Projects and Next Actions with email folders and messages instead of tasks. FWIW, here is what I do...
I have an @Projects (email) top-level folder that contains one subfolder for each GTD Project I have. Any email related to a Project gets moved into the corresponding subfolder.
To create a Next Action, I send myself an email message. I use the category to indicate the GTD context: @office, @home, @errands, @waitingfor, etc. For @deferred I set a Follow Up flag with a reminder time. I also set a category for each Next Action that is to be taken face-to-face, say at a regularly scheduled meeting (@Alice, @Bob, etc.).
Common (potentially tedius) tasks involve filing messages (including Next Actions) from my Inbox into the appropriate @Projects subfolder and setting the context (category) for Next Actions. I use Outlook with NEO (the Nelson Email Organizer), a front-end that indexes messages for fast retrieval in a variety of ways. NEO has lots of nifty features, but the main advantage with respect to GTD is the way it handles categories and folders. Using a few keybindings and pop-up dialog boxes, it is very easy to assign a category to a message, retrieve messages by category, and move messages to Project subfolders.