I have just acquired a secondhand iMac - model A1225 8,1

I can not install OS X on it though. It has a kernel panic everytime I try. eg; initial start of install ends with 'You need to restart your computer' etc

Here is what I have tried:
- All Hardware diagnostics passed
- Reset PRAM
- Reset SMC (running SMC 1.30F1)
- DVD Snow Leopard
- DVD Leopard
- USB SL
- USB L
- Grey installation DVD
- Target mode install
- Swapped RAM with working iMac (RAM works in other iMac, other iMac's RAM still gives same errors)

All end with 'You need to restart....' kernel panic.

The strange this is that I CAN install windows 7! It will run install and run Windows 7 but only 32-bit mode. Windows 7 64-bit will not work either.
Windows 7 32-bit OK!
Windows 7 64-bit fails

Latest thing I have tried is a full install of Snow Leopard using FW Target Mode. This worked and I can boot my good iMac from the HD in the bad iMac! This means the HD is correct with a good OS X.

Still won't boot on the bad iMac though :-(
It must be the EFI?? That is what I think.

I can boot in single user mode (Apple-S) though.

Any way of sorting out the EFI on the iMac 8,1 model?? It is the only one not listed anywhere! I have a good working iMac (also an 8,1) if anyone knows how to copy the EFI over???

Thanks
Paul