Right, the firmware won't allow one to boot from a earlier OS X version than what came on the machine.
I have a new macbook pro which I bought with Lion pre installed
If this machine is a Early 2011 or earlier, then it can be downgraded to 10.6 Snow Leopard, Late 2011 or later cannot.
It's a matter of hardware drivers and Late 2011+ machines don't have their drivers in 10.6 or the 10.6 combo update.
Download the free MacTracker and use the Apple Menu > About this Mac > More Info to make sure of your machine.
I have an original disk of Snow leopard.
There are two basic types of Snow Leopard disks.
1: Snow Leoaprd white retail disks that have 10.6.3 on them
2: Colored machine specific versions with the free iLife package on them.
The colored machine specific disks must match your model exactly as they contain hardware drivers for that particular machine model only.
The Snow Leopard retail disks only work on Intel Mac's that came from the factory with 10.6.2 or earlier installed.
Mac's that came from the factory with 10.6.3 or later installed need the 10.6.3-10.6.8 machine specific disks.
However it's possible to take a image of the 10.6.3 disk and combine it with the 10.6.8 combo update to create a new boot disk. This is a old thread on the subject.
How can I make it happen?
The firmware on the Mac is going to prevent you from booting from the 10.6 install disk if the machine came from the factory with 10.7 preinstalled.
To get around this you need another Mac that is capable of booting from the 10.6 disk and use Firewire Target Disk Mode to install 10.6 on the factory 10.7 Mac.
Once 10.6 is on the drive, it will boot. However a clone won't boot and reinstalling is always going to be a pain as one needs another Mac capable of booting from the 10.6 disk.
So your going to have to do this twice on two internal drives, this way you will have a extra 10.6 internal boot drive to put into the machine if you have problems with the first one.
Andreas Skordis wrote:
I already tried booting through Recovery HD and booting from the Snow leopard disk is not an option since it doesnt allow me
Well Command r booting into Recovery HD partition isn't going to help as it's 10.7
If you can hold the option key down and select the 10.6 disk to boot from and it works, then you have a Late 2010 or earlier machine and just need to use Disk Utility to erase the ENTIRE drive (prefereably with Secure Erase > Zero) and quit and install 10.6.
Another option you might want to consider if your machine or your capabilities doesn't meet up with I outlined above, is to run 10.6 in a virtual machine program in 10.7.
It's a "hack" , the performance isn't going to be quite as good as a native boot, but it works.