Hi mate,
You'll have to go in the boots folder, take a random pair of boots, import the file on pssg editor and export it as a bitmap (I think - it's been a while since I last modded anything - or you probably have to export it as a dds file via pssg editor then use that file as an input for DXTBMP and extract a bmp file from there). Then use it as a template for your new boots. You'll have to find a few good resolution pictures from at least five angles (top, bottom, inner foot, outer foot and heel) then import them as new layers in your favorite pic/graphics editor software (I'm using Gimp but if you have Photoshop, go for it) on top of the template. Then it's a matter of fitting the different views as best as you can on the template. I personally try to fit them by increasing and reducing transparency in order to fit every notable feature (laces, bootstraps, Adidas logo, whatever suits you). Use the cage tool to deform each layer and overlay them on top of the template. Then when they fit nicely, you'll have to use the eraser or finger tool with a blurry edge to smooth out imperfections. When you've done it for one shoe, use the duplicate and mirror functions to copy the result onto the other side. I'm a perfectionist so I can spend too much time on a pair but lots of modders here can do a pair of boots in an hour or even less. The most difficult part IMO would be finding the right pictures. If you create Adidas shoes, you can refer to their online shop and download the high res pics by right-clicking on them or on the page, inspect the html code and find the picture. I also use that technique when looking for high res reference pictures for jerseys when I need to nail their texture.
I'm saying all this from memory, so you'll have to proofread that method for me by testing this tutorial. Do not hesitate to bring possible improvements and share them here.
