From my personal experience so far, I've come to find that there's not much of a pre-production support structure in the Machinima community as much as there is a post-production capacity, in that it's easier to get critique and comments on your machinima projects after they've been competed and released compared to getting technical advice or help when you're first creating your project. When trying to find a specific tutorial or guide to modifying an aspect of game (such as Half Life 2) with creating a machinima in mind, it can be rather difficult. This is mostly because there's more of a focus on modifying the game for single or multi-player gameplay.
While there are sites like Machinima.com, which do have articles on the basic theories on creating machinima or modifying some of the games commonly used for machinima, there doesn't seem to me to be a central 'hub' of sorts, with guides, articles and tutorials aimed specifically at creating machinima. I sometimes wonder if someone were to create a kind of "How to make Machinima" super website with more focus on the overall creation of machinima rather then just the critique of finished films, if it would be a helpful addition to the machinima community as a whole.