Firstly download a skin which u like (there are a lot of good one around on this forums)
when u have got one extract it if u need to and place the folder in
C
Documents and Settings\Rav\My Documents\Sports Interactive\Football Manager 2008\skins
then load up FM2008 and go to options => Preferences => Display & Sound. where it says skin click on the drop down arrow and it should show the skin which u placed in the above directory.
on the right of that Untick Use skin Cache and tick Always Reload skin on Confirm
if u do all this it should work
(if im wrong someone correct me

)