Installing Leopard from DVD: Apple logo? I need to install Leopard OSX on my mac. 

When the mac starts, I hold the alt button and I load the Leopard Installation DVD. Afterwords I can only see the Apple logo on the screen and everything seems stuck (waited for 8 minutes so far).

How much am I supposed to wait to see the first istructions when loading the Installation DVD at boot time ?

thanks
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.).