Install OS X 10.6 of a Mac Pro 3.1 8 Core (Early 2008)

Hello.

I have a Mac Pro 3.1 with 2,8 Ghz + 8 Core (Early 2008)

and 14 Gb RAM and 3 HD's. HD1 500Gb, HD2 500Gb, HD3 250Gb.

At the moment i is installed OS X 10.8.3 on HD1. Now I would also install the OS X 10.6. It is possible on this mac right?

I must it install only on an other Harddisk perhaps HD2, right?

When I have startet OS X 10.8.3 and then I would start the file "Mac OS X 10.6.0 Snow Leopard Retail DVD.dmg" then it comes a window but there I cant start the file Mac OS X Installation.app. It has in front of the Icon a Symbol that means that I cant start it.

What must I do to install the OS X 10.6?

I have a file on the mac: file Mac OS X 10.6.0 Snow Leopard Retail DVD.dmg

and I have a DVD MacBook Pro Mac OS X Install DVD from my 17-inch MacBook Pro (also 10.6)