   Getting started with a 3D Tower Defense game
  Hello, I've been interested in XNA for a few months now and have gotten started ever so slightly. I know how to make moving, animated sprites, write text etc. in 2D but that's pretty much about it. I've been reading here and there about starting with 3D games but I can't quite seem to get anything done. The 2 main things that I'm trying to do right now (I guess these would be the best ones to start with) are the camera (I know how the vectors work, but I'm having a hard time grasping the whole Matrix-thing) and a grid system for the towers, which I really don't have any idea how to do yet. From what I can find by googling (although I wouldn't say that I'm a great googler, really) is mostly 2D Tower Defense-related tutorials, there doesn't seem to be much about the 3D variation.So, basically what I'm asking for is pointers as to how to get the project started, even if just a little. :)   
  Assuming your game is basically 2D, but with a 3D camera (i.e., 3D graphics, but not 3D game), it won't be much different than the 2D one, when it comes to tower placement. Towers will be places using a translation matrix to the relevant position in the grid. If assuming Y is up (a lot of games do), then a 2D location of (x,y) will become a 3D location of (x, 0, y). This assumes all the game takes place on a 2D grid whose height is 0.   