Another way to see how your UV mapping is going (and you will also need this later on when you are painting your textures in Photoshop or simmilar) is to select the Edit menu in your XSI Texture Editor (shortcut for the TE is usually Alt-7) and then select "Stamp UV Mesh". You will be asked if you want to replace the current material with the new one, select yes and then you will be able to use render preview or render areas ("q") to see how your UV mesh looks on your model directly.
To start making a UV map itself:
1. Select your model, then go Model->Property->Texture Projection
2. Select any projection, I usually go for the top-down
3. Prepare a full black "canvas" image in your image editing program. I recommend higher resolutions because you can always scale them down later as needed whilst enlarging low-res images tends to go blurry
4. Again go Model->Property->Texture Map
In the Clip section of the window which pops up, select New->From File and then pick your black canvas image. This will make it easier for you both to arrange your UV mapped sections and to paint them later on.
5. Press Alt-7, this should take you to the Texture Editor.
Move your UV mesh outside of the mapping area which should look like a black square.
Minimize or close the TE and select a few polygons with the raycast polygon selection tool ("u")
6. Open the TE again. Depending on the selection you made and its general shape, choose either Planar, Cylindrical or Spherical subprojection (bottom row on the top toolbar) and then select the alignment which gives you the most fitting shape. Keep in mind this - the greater the angle of projection to the actual surface you are UV mapping, the more "stretched" the final texture will look. So always aim to have that angle as close to 0 as possible. With practice you will get the hang of it.
7. Scale, rotate and align the new UV mesh section on your canvas. As you will end up with many such sections, I recommend just placing them on the side of the canvas area and adjusting their size and position later when you have all the pieces mapped. Keep the UV maps of big sections of your model which require higher resolutions as large as possible since if you have (for example) a big flat surface mapped to a tiny section on your canvas, you will not be able to paint it in sufficiently high resolution and it will look grainy and ugly. Small, unimportant or "low-visibility" sections you can fit in last, in spaces that you have left on the canvas even if it means scaling them down a lot.
8. When you are done arranging the sections, go Edit->Stamp UV mesh and select the file name of your brand new skin texture file. Select yes when the program asks you if you want to replace the current material. You will then need to open that image in your image editing program, and then, using the UV grid "stamped" on it, paint the texture as you wish.
And that's the basics. There are a few more tricks, like using Tools->Match to match the UV grids of symmetrical parts, making them overlap and thus having to paint over them only once to cover both sides of the ship, Tools->Heal to join up two or more UV sections together and avoid seams between then (this is how you UV map an organic or continuous texture, for example a face) or mapping just one half of your model and then using symmetry to complete the model and so on, but the above should get you on your way.
Experiment and expect a lot of frustration at first since this requires a bit of practice to get the feel for it. Good luck!
