I can help you if you're using XSI Mod Tool. Select your object, then click the Texture button on the left side. It will bring up a menu, and you'll want to click Image. At the top (where it says nolcon_image), you'll want to add a new image, from file. You can just use the vtf here, no need to convert it. Finally, go down towards the bottom and select a projection. It most likely doesn't matter what you select because you'll probably want to tweak it anyways.
To tweak the projection, select to the surface you want to alter. Then open up the Texture menu again and down at the bottom press the Projection button. There are lots of choices here, and you'll have to get used to it. My advice to you is to, with your surface selected, press the cube button towards the top and click Best Fit from the drop down menu that shows up. Then you can use the normal movement hotkeys (C, V, X) to rotate, translate, and scale. You can also hit space and select just individual points to move things around.