Not every skinn that you download will show up I'm not sure why but some will work some won't.
Download this before you download any skin as you will need to extract the skin. This software will help you to do that.
WinRAR (32-bit) - Free software downloads and software reviews - CNET Download.com Then look in
C:\Users\yourname\Documents
Then open the sports interactive folder
C:\Users\yourname\Documents\Sports Interactive
Then open the
C:\Users\yourname\Documents\Sports Interactive\Football Manager 2012
Then you will prob not have a skins folder so you will have to create one, you can do this by clicking on Organize which is in the far corner next to Views then click on add folder and call that folder skins when you have done that this is the folder you want to extract your skins in
C:\Users\yourname\Documents\Sports Interactive\Football Manager 2012\skins
Then open up the game then go into preferences on fm12 then display and sound and your skins should be there. . .hopefully.