Q: Need Help Installing Snow Leopard over Mountain Lion!!!!

Really? You should try installing Snow Leopard over Mountain Lion.

You get a message saying that the SL disc is incompatible with the ML installer.

You get a message saying that the SL disc is incompatible with the ML installer.

You would only get that message if you forgot to boot from the Install DVD - or if the computer can't use the Install DVD and defaults back to the hard drive OS.

Yep .... well almost. I didn't forget ........ I CAN'T boot from the Install DVD, as I explain in my original post.

From what I have read, people seem to be able to install Old over New by simply loading the Old install disk in New and Old will be dropped over New. You cannot do this with SL when you are using ML because the SL installer will not run in ML. (I got it slightly wrong). Therefore you have to try and boot from the Snow Leopard install disk, which I cannot do.

I suspect that this is because I am using an iMac which has a Bluetooth keyboard and Mouse. By the time the Bluetooth wireless software is activated and transmits the "CMD + R" keys, or the "C" key, or the "Alt" key (On UK Keyboards it's Alt, not Option), or whatever, it is too late. The startup process has passed the point at which the manual startup key depressions are processed.

Having investigated this further, it seems that the Bluetooth keyboard and mouse can cause a number of problems around startup and wakeup (after going to sleep). Back In The Day, I had similar problems with infra-red keyboards and mice.

I have a USB keyoard, but it's a Windows layout and does not seem to respond at startup in ways that OS X understands. I guess I'll have to buy a USB Apple keyboard and give the Bluetooth one a Viking Funeral. Maybe, while I am at it I will scrap OSX (it's going to become a glorified iPhone) and install Ubuntu.

I don't think USB keyboards respond that differently. At least not for C key or Option(Alt) key.

With S.L. DVD in, if you restart and hold the Alt(option) key immediately after the gong sound, do you get a "menu of icons" that includes the S.L. disk?

WIth another Mac available, you could make a USB install key:

http://www.maketecheasier.com/create-mac-snow-leopard-usb-installer-disk/2009/10 /08

You didn't tell us the exact model iMac, and whether you're using the original restore DVD or a retail DVD. That can make a difference - the retail DVD may not have the driver(s) required by the model of iMac.

And for future ref: You've tagged onto another's thread. Usually results in some confusion, and doesn't give you all the attention you may need. Better to start a new thread.

Put in the DVD.  Click the apple >> system preferences >> startup disk >> select DVD >> restart.

http://support.apple.com/kb/PH10603

- the retail DVD may not have the driver(s) required by the model of iMac.

Sorry if that was a little obtuse...

I meant to say - the retail DVD may not have the driver(s) required by your model of iMac. There are some iMacs that are newer than the retail S.L. DVD.

That's not true, as long as the Snow Leopard disk is available and meets the hardware in the newer macs, the newer macs can most defintiely run it. One would just have to know what they're doing.

delete

Not recommended - see the linked Apple support article.

Install OSX Restrictions