Go into My Documents/Sports Interactive/Football Manager 2008/Graphics/Backgrounds
(You may have to make a Graphics folder then a Backgrounds folder inside your newly made Graphics folder).
Once you have done that, make another folder and name that Default.
Now inside your default folder, Place your picture inside and name that default as well.
Now you need a config file.
Download this file, unzip it and place inside your default folder alongside your default picture.
Now open up your game, Go to,options, Then preferences, Then display&sound.
Check to see if Skin Cache is unticked. If not, Untick it.
Check to see if Always reload skin is ticked. If not Tick it.
Now check to see if Show Backgrounds and logos is also ticked. If not, Then tick it.
Now press confirm.