I am trying to install Mac OS X 10.6 on a 17" MacBookPro 4.1 with a Core2 Duo. But the install says:
Mac OS X 10.6 cannot be installed on this computer.
Any ideas why or, better yet, workarounds?
There are two options
You are trying to upgrade from a version that is not Leopard , or an early version of Tiger (< 10.4.4, according to the SL DVD I have). If so, back up your data to an external drive, format the MacBookPro's drive and make a clean install. This should work even if you only have an "upgrade" SnowLeopard DVD.
You are using an install disk that accompanied another (more recent) Mac. In this case, rip the disk, use "Show Package Contents" on the installer and find the file Info.plist. If you have Xcode installed you'll have access to Property List Editor.app, but you can also edit Info.plist in any text editor. What you'll be looking for is a key-value pair that is used for checking the install restriction. Change the value, save, and burn the image onto a DVD (or for speed install from a USB stick, but that needs some more steps).
Since Apple changes the install disks every now and then, this procedure may not work exactly as described, but you get the general gist of it.
Sometimes this has to do with the version of the disc versus what the hardware shipped with or what it expects. Are you using the install media that came with the machine or something newer?