I'm out of ideas here.
MacBook Pro 3,1 with a Core 2 Duo and 10.5 isn't booting an OS X Lion DVD. I get a grey circle with a line through it then the Apple logo immediately.
I've zapped the PRAM - no good.
fcsk -fy - no good.
Restored the DMG to a FireWire hard drive - no good.
Restored the DMG to USB and tried booting - no good.
Repaired Disk Permissions with Disk Utility.
There's no Boot Camp partition on it. I tried a Snow Leopard DVD - same results - circle with line through it and immediately to the Apple logo.
The Lion DMG is mine from my < 1 year old Core i7 MacBook Pro that I downloaded from the App Store.
Checked for updates to SMC and EFI - it's up to date.
Tried changing the startup disk in Utilities - asks for the admin password and then beeps at me with no reason.
When I go into the DVD / USB from inside OS X the installation program has the same grey circle with line through it over its icon.
The laptop is fine - he's (my father) been using it for weeks in 10.5 - doesn't care if it's completely formatted; just wants to get the latest OS.