Here are the official system requirements for Football Manager 2011 announced by Sports Interactive Games.
OS - Windows XP/Vista/W7
Processor - XP : 1.4GHz or Faster, Vista/W7 : 2.0GHz or Faster
Supported Processors: Intel Pentium 4, Intel Core, AMD Athlon
Memory - XP : 512MB RAM, Vista/W7 : 1.0GB RAM
Hard Drive Space - 2GB
DVD-Drive - 4x Speed
Video Card Memory - 128MB
Supported Chipsets - Nvidia FX 5900 Ultra or greater; ATI Radeon 9800 or greater; Intel 82915G/82910GL or greater. Earlier cards may only display 2D Match Viewer Mode and are not supported. Laptop versions of these chipsets may work but are not supported.
Sound Card - DirectX 9.0c compatible
DirectX - Version 9.0c (included)
OS - OS X 10.5.8/10.6.x or higher
Processor - Intel Processor
Video Card - Nvidia Geforce 7300 GT or greater; ATI Radeon X1600 or greater.
If you doubt whether your computer is enough for playing Football Manager 2011 try to download and install the demo. It will help to solve such kind of issues.