Has anyone tried to re-integrate the CSM (BIOS compatibility support module) into the iMac's EFI?
TianoCore's EFI distribution includes a CSM module for EFI. If someone has a BIOS image in the necessary format, someone could try loading the CSM EFI module (from within the iMac's EFI shell) and try to install Windows.
BIOS support seems to be the only problem in the way; the iMac supports ACPI and OS X actually uses it.

As we've found out in other threads, it is pointless to try to load Windows XP or Vista in EFI, since neither fully supports EFI and GPT-disks.

This sounds like a good idea. Has anyone tried this? I might, if someone can provide instructions.

CSM isn't something that can be "re-integrated" or "loaded", it is by necessity an integral part of the built EFI image in much the same way that your circulatory system is an integral part of your body.

To try to clear the air on the subject a little, here's a cut and paste from the TianoCore acronyms page:

Compatibility16: A traditional legacy BIOS with the POST and BIOS Setup code removed. Compatibility16 BIOS code executes in real mode

Compatibility BIOS: The combination of both EfiCompatibility and Compatibility16

CompatibilitySmm: Any IBV-provided SMM code to perform traditional functions that are not provided by EFI

CSM: Compatibility Support Module. The combination of EfiCompatibility, CompatibilitySmm, and Compatibility16. Portion of the Framework that allows compatibility with non-EFI compliant operating systems to run on Framework firmware.

I am pretty sure it could be re-integrated. It is just like an EFI module or driver, which can be loaded from the EFI shell.
And I don't know what you are trying to prove with your copy-and-paste from TianoCore.

mk14, what makes you "pretty sure"? Do you have evidence, or are you just engaging in wishful thinking?

I encourage you to download the freely available EDK sources from the TianoCore website and look for yourself. The code that implements the interface to the individual items I enumerated in the cut and paste above is intimately intertwined with the EFI sources; it is not "just like an EFI module or driver".

In addition, as has been pointed out elsewhere, the TianoCore distribution does not actually include either the Compatibility16 nor CompatibilitySmm components, both of which are tightly coupled to the platform hardware.

Can you stop flaming? Everyone is trying to help.....