The older Core Duo Mac series cannot boot into 64-bit operating systems, and is excluded from modern versions of OS X, but Microsoft still supports 32-bit processors, giving many old Macs the opportunity to be re-purposed with a modern OS. I can confirm that if you use Boot Camp to install Windows 7 32-bit (no key needed) on a Core Duo Mac Mini, you can upgrade to Windows 8 32-bit from within Windows 7, and then do the same for Windows 8.1 (provided you have a license key for the final OS). Boot Camp 4 drivers work well for the 32-bit Windows 8.1, but I installed each one individually instead of using the BootCamp package installer. All of the hardware functions; however, I have not installed the Boot Camp shortcuts for startup disk selection, or for the onscreen display of volume and brightness controls.
I'm not sure if this is much of a tip, but the Windows 8 install disk freezes on a CD-ROM selection screen and I haven't seen these tips anywhere else online. I've read that new Windows 8 disks have a specialized MBR that doesn't work with older Macs, and EFI boot was added to Macs built much later.
I have replaced this Mac Mini with a much more capable iMac, but I like that the old computer can still serve a purpose. Sometimes, it's really convenient to have a Windows PC close by, even if it is not needed every day. It's even better when that Windows PC is a Mac. It's also nice not to have to restart into Windows 8 on my main Mac.
P.S.- Right now, this Mini is acting as a HTPC in my living room with a Bluetooth keyboard/trackpad, and a Windows MediaCenter remote and ATSC tuner.
[crarko adds: As someone with a lot of older hardware still around, I appreciate ideas like this. Never been a huge Boot Camp user (preferring virtualization) but I see where this could come in handy.
Note to all: I'm back again for a while, and my hope is to try to post something every day. I know the site has been pretty slow, and your continued help by submitting your hints and ideas is always very welcome. Thanks. -- Craig A.]