Can I install 10.4 over a later OS

[GGD]

WHiiP wrote:
The general rule of thumb is that you cannot go backwards on a machine that came with its OS. Obviously, you could buy a used machine that has OS X.6 on it, but it originally shipped with OS X.4, then YES you can go backward to OS X.4, but NOT OS X.3

One catch is that if it's an Intel Mac from 2006/2007 that shipped with 10.4, you'll need the install disks that shipped with it. The retail 10.4 disks were PowerPC only.