The problem I have with using iCal tasks for my action lists is that, unless you have a program that handles the next action concept for you, you end up with a jumble hodgepodge of crap you can't do yet because you have all the actions from your projects in at once. Of course, all the GTD apps out there such as iGTD, the forthcoming OmniFocus (which looks great, btw), Midnight Inbox, ActionTastic, are all just list managers. You can do the same thing in plain text, MS Word {shudder}, OmniOutliner (with or without kGTD), or any of the online apps such as Stikkit, Remember the Milk, Backpack, or any of the slew of wikis available to run online or on a USB drive. Now you just have to choose one.

If you want to continue to use iCal, I would suggest doing your project planning, where you outline all the steps for completing the project. Then, at some comfortable interval, add new NA's to your iCal tasks. The trick here is to not let your projects languish between your review of your project planning material for lack of having a NA in your task list. For this reason, I would recommend a daily or every-other-daily review of your projects.

Another solution would be to have a calendar for each project in iCal. Create all your tasks there as a project planning space. As new NA's come to the fore, you can just change the calendar to the calendar for the appropriate context. If you create a calendar for each project, do put them in a calendar group so that you can easily turn those all on and off at once and they won't clutter up your "real" calendars. It'll save a lot of hassle.