How to Downgrade from 10.7.2 to snow leopard

Hi

My customer bought a new imac, it turns out he got a 12.1 iMac Mid 2011. With system 10.7.2. Printing machine can only be installed on the system snow leopard. how to downgrade as well. because if the downgrade by using Original iMac 10.6.7 installer. system cannotUpdate .. application also can not be installed (iLive) and also update to 10.6.8 stuck. ... please help

Ok