First off, the squash, potatoes and carrots all need to be cooked until they are quite soft. You can bake the squash, halved, in a pan with a little water at 350 for about an hour, or you can peel it, cube it and boil or steam. Cube and boil the potatoes, and steam or boil the carrots. If you steam anything, reserve the water to use in the soup.
While the veggies are softening away, chop and sauté the onions until translucent, adding the garlic for just a minute or two to soften.
Next, puree everything in a food processor (you can reserve a few potato chunks to add texture to the finishe'd soup if you want). Then add it to a soup pot and mix well, adding water to the desired consistency (remember that you still have a cup of soy milk coming), bullion and spices. Let it simmer for at least 15 minutes, then add the soy milk and heat through. (add the potatoes now if you reserved any). Adjust seasoning, and enjoy!
Of course, soup is not an exact science, so feel free to add more or less of anything :).