Installing Leopard from DVD: Apple logo?
You most probably won't be able to install this OS X version on your iMac:


10.6.4 (which is Snow Leopard, not Leopard) was released June 15th, 2010 (Wikipedia)
iMac 12,2 was released mid 2011 (Apple Support Document)


As a general rule you can't install older OS X discs on newer hardware (missing drivers etc.).