Same spec as any MCE machine. You need to check your graphics card against the approved list. If its an ATI or Nvidia you can look on their websites. Dell's MCE laptops can be quite cheap and they only charge about 35 quid extra for MCE.
Even if its a too low spec graphics card, I believe that there are ways of fooling MCE into thinking its a higher spec one. Try The Green Button website or the Australian Medai Centre community site if you need to do this: http://www.xpmediacentre.com.au/