Step 1: Pitch the idea.
If you're a one man band you really don't have to do this. If you're trying to woo others to your cause, putting together a range of storyboards, paintings, and story ideas would really help. There's an extra on the first season of "Spongebob Squarepants" where they talk about how Stephen Hillenburg pitched the show, and there's a tiny bit of this mentioned on "The Incredibles" as well. It is more than a PowerPoint presentation. In fact, do not create a PPT slideshow. This calls for a very simple effort: make pretty pictures you can control and talk about. Personally, I'd use iPhoto, or maybe Galerie to create a simple slideshow of art that goes through the vision for the film. I'd recommend iWork for Keynote's great slideshows, but it's $80. And when pitching your flick, remember this rule: sell the sizzle, not the steak. [Thanks Dr. Hinton]
Step 2: Story treatment.
This is where you write up story ideas, start putting them together, and hammer out the structure of the film. All you need is a word processor. TextEdit, TextWrangler, Open Office... Choose your poison.
Step 3: Storyboards.
In my DIY ILM post I mentioned Director's Boards. There's a free version, and it works. Storyboards really work better when printed and arranged on a giant wall (which is the way everyone does it anyhow), so I'd just suggest you find the cheapest printer you can find. Better yet, just draw them on pieces of paper... Don't know how to draw? You can learn. Pick up "Drawing on the Right Side of the Brain."
Step 4: Record vocal talent.
If you absolutely have to, recording should be no problem. Jump into a closet full of heavy coats, or a soundproofed room and fire up QuickTime Pro. It's only $30, which is a heck of a deal. Now you can record your audio. I guess if you're really cheap you could use Audacity.
Step 5: Editorial reels (layouts).
This is where you see the little storyboards moving around, timed to the audio you recorded. This is the first look at your film, and here you see if the direction you're going works. Pacing, framing, and structure are what you should be refining at this point. I suggest using iMovie for this, as you can always record more audio if you need it, while watching your images move around. This is sort of a rough cut at this point...
Step 6-13: The modeling, animation, lighting, texturing, and rendering process.
So here's where you get locked into a cage and don't see the sun for months on end. Project Orange is using Blender 3d, a free, open source 3d tool for their project. It's good. In fact, it's amazing. The fact that this remains free and OSS to this day is a testament to the power of OSS. To learn Blender properly however, you should really buy the manual. Good news is, each manual goes to the Blender Foundation, which keeps it alive. We have mentioned Blender before. That interface bugs a lot of people, but take it from me, once you learn how to move in it, you'll be animating very quickly from there on out... Well, as quickly as 3d animation will allow.
Step 14: Editing, adding music, effects, and distribution.
For editing, you've got iMovie. For music, there's GarageBand. But you knew this, didn't you? Effects can be handled inside of Blender, to an extent. If you really need compositing, you could download and "try" a demo of After Effects, from Adobe, or Motion, from Apple.
Pixar doesn't distribute their movies, Disney does. Distribution is a top-heavy industry, with millions sunk into P&A: prints and advertising. The physical cost of creating the film prints is exorbitant. I say either create DVD's on demand (sold through an online store), or distribute digitally, using say, DTV or even the iTunes Music Store. Then wait for the big-time Hollywood offers to roll in, you little John Lasseter.