Try Clint Bellanger's isometric math tutorial: http://clintbellanger.net/articles/isometric_math/ (second time this week I've linked to that tutorial! ). That article was the key to my current understanding of isometric perspective/math, and I've used it myself and seen it used in real-world applications, so I can vouch for the accuracy of the information it gives.
Wow! That's really easy to understand o.o Thanks!
I'm pretty sure that'll do it. It says that it's "Tiles Math" but regardless I think it'll be fine. I'm not sure if what I'm doing will be tiles, or actually what it will be in general. It's just like.. one solid piece of land. And I would generate a new one each level.
EDIT: Also referencing what FLeBlanc said about orthogonal projection, when I look up anything about Isometric perspective and changing the camera with XNA that always comes up now. So maybe what I want is a tutorial for projection?