Hi Ali,
It's been my experience that the iFixit staff put out so many guides that it's impossible for them to cover every single aspect of every device they make guides for. I suspect that since trackpads rarely need to be replaced, that puts making a guide for it down on the priority list for guides that they feel are needed.
That being said, I understand that you still need one. As it turns out, it's a pretty easy repair, all in all. Once you have the battery out, there's four Phillips screws holding it in, so all you have to do is take them out, disconnect the ribbon cable and drop the trackpad out of the cover. You can follow the iFixit guide for removing the battery to start with.
[guide|1712|MacBook Pro 15" Unibody Mid 2009 Battery Replacement - iFixit Repair Guide|new_window=true]
That'll get you 80% of the way to getting the trackpad out; here's a YouTube video that shows the entire procedure.
[link|https://www.youtube.com/watch?v=APxbp-Cieg8|2009 Macbook Pro 15" A1286 Track Pad Replacement - YouTube|new_window=true]
You shouldn't have any trouble fixing your MacBook now. Good luck, and let us know how it goes!