I have a 22inch widescreen Samsung monitor and it looks PERFECT like this.
1) Copy and paste this info below IN FULL. 2) Right click on your desktop shortcut for FM 2008. 3) This will take you to shortcut properties. 4) Paste the below into 'Target' on first screen. 5)Ta da! Perfect fullscreen FM 2008!
You can adjust the numbers at the end (1280 and 800) if this fails to work. Perhaps look at another of your games and see what resolution it uses.
"C

Program Files\Sports Interactive\Football Manager 2008\fm.exe" --fullscreen_width=1280 --fullscreen_height=800