Actually XSI does have a polygon reduction tool. Since I don't have the software where I am right now, under the help menu, in the search box type in Polygon Reduction tool :). From what I remember though, it should be under Modify -> Poly. Mesh -> Polygon Reduction, and of course make sure you are in the "Model" view.

I don't have XSI in front of me to double check, but if I remember correctly (I haven't used that feature in a while), under the model tab, under the create module, click the poly. mesh button, and it should be there, extrude along curve. If it's not there, just use the help menu and search for extrude along curve, and it will tell you ...

As Erglegrue has mentioned, the toon effects you applied do not export with your model. You will have to get or code your own shader and use it with XNA. As for your texture you painted, correct me if I'm wrong, but I do believe you need to add the texture you applied on it to the Content directory where you model is so it can read it. If that ...

If you are going to build a 2d space sim, UnrealEd would not be a good choice to build maps, as it is used to create 3d maps. If you are going to make a 2d game, then you could use any paint program available to you to create your sprites, tiles, background images etc.  Also, I haven't used Unreal Ed, so I don't know what file format ...

The way artists do it depends on the level of detail they need to achieve. Usually for final fantasy 1 characters, or characters that are 16x16 or 32x32 are usually done pixel by pixel as they are too small to trace an image or add lots of details. Characters like the street fighter characters are usually drawn on paper first, then traced in a ...

Here is another good one, the Joan of Arc Tutorial. Joan of Arc Tutorial There are a lot of other good tutorials on 3DTotal not to mention a lot of tips and articles on how artists built their models and scenes that you may want to look at.

Well since I'm at work, with not much to do, I decided to do a little searching around. These tutorials are not XNA specific, but should give you a good head start on how to achieve an isometric tile-based world, along with tile-based calculation algorithms. Isometric Coordinate Calculations  - Simple algorithms for "Map to ...