Installing UEFI for Windows 8 and dual booting with Mountain Lion can't be done using Chimera / Chameleon as the boot loader - they cannot see the Win8 boot files partition. No matter how you install them, the first thing you need to do is boot to BIOS and make settings for OS X install, AHCI, SS3, HPET 64 bit, etc. as required - save&exit & continue boot. For specific BIOS settings refer to your mainboard manual or to one of the many threads in User Builds or Golden Builds forums. Most give BIOS settings and MultiBeast settings. EDIT: While the title says Windows 8 and Mountain Lion, it works the same with Windows 7 or Windows 10 and Mavericks or Yosemite or El Capitan. Installing on separate drives. (Recommended method) When installing on separate drives, installation order does not matter. Start with either one. Installing Mountain Lion Disconnect all drives except the ML drive-to-be. On a factory blank drive, use disk utility in the OS X installer to format it GUID and partition the drive as you wish with Mac OS Extended (Journaled) for your boot partition. Note that drives larger than 1Tb still need a boot partition of less than 1Tb. Installing on a used, re-purposed drive I like to zero it out first. In the ML installer disk utility, first select the drive in the left pane and the Erase button in the right pane. Click on the Security button and move the slider to write 1 pass zeros. This will take a while to complete depending on the size of the drive, so if your drive is 2Tb and you don't have a couple of hours to wait, then skip this step. Just partition the drive as you wish and procede. Once your drive is partitioned, use UniBeast to install OS X. Run MultiBeast to get your post install kexts added for your mainboard. See http://www.tonymacx86.com/61-unibeast-install-os-x-mountain-lion-any-supported-intel-based-pc.html Installing Win8 Disconnect all drives except the Windows 8 drive-to-be. When you boot Win8 install DVD on a UEFI BIOS mainboard, Win8 wants to install UEFI. Unfortunately, if it does this Chimera/Chameleon can't "see" the boot files. There are at least 2 ways to prevent this. One way, when you boot with the install DVD in the tray, hit F8/F11/F12 or whatever the Function key is that allows you to select a boot device during the BIOS POST. You will find that your DVD shows up twice - once as SATA and once as UEFI. Choose the SATA. You do not want the UEFI. Another is to disable UEFI in the BIOS. Some BIOSes have an option for boot mode with the selections: Legacy, Legacy or UEFI, UEFI. Selecting the Legacy option forces non EFI installation. For a complete install to use all of the Win8 features (recommended), at the select partition screen of the installer, delete all of the partitions, select the unallocated space and click Next. The installer will take it from there. See http://www.eightforums.com/tutorials/2299-clean-install-windows-8-a.html?filter=Installation%20and%20Setup Note: If you do not want the System Reserved partition, then pre-format the drive with the C-partition-to-be MSDOS FAT with OS X disk utility, then format it NTFS when in the Win8 installer or use your favorite 3rd party disk management tool to partition it NTFS, then install Win8. When you have both your ML and Win8 installed, shutdown, connect all drives, boot to BIOS and make the OS X drive first in HDD boot order. At the Chimera timeout screen you can hit a key to select the System Reserved icon, you can change the string value of the Timeout key in org.chameleon.boot.plist to 0 seconds (effect is same as Instant Menu) or you can install Instant Menu and it will wait at the boot screen for you to select an OS to boot. If you installed without the System Reserved partition, just boot with the Windows NTFS icon. With Windows installed, if I installed OS X first, I usually boot OS X and run the Chimera installer again. Now that the Chimera installer sees you have a Windows drive, it installs the bootMD instead of boot1H. ------------------------------------------- Installing Win8 and Mountain Lion on the same HDD After partitioning your HDD in OS X disk utility (or your favorite 3rd party disk management tool), you can install Mountain Lion and Win8 on the same HDD in any sequence and order: Install Win8 first on first partition and then Mountain Lion on later partition Install Mountain Lion first on first partition and then Win8 on later partition as long as it is one of the first 4 partitions (including the OS X EFI partition). Install Win8 first on the second or third partition and then install OS X on the first partition Install OS X first on the second or later partition and then install Win8 on the first partition To install Win8 first to the first partition: 1. Boot UniBeast to the OS X installer and format the HDD with this scheme: GUID partition tables first partition - for Win8, size as desired, MSDOS FAT second partition - for Mountain Lion, size as desired, Mac OS Extended (Journaled) any other partitions you want, size as desired, format as desired 2. Once partitioning is complete, exit installer and reboot with the Win8 install DVD in the tray. 3. At the install screen, select the first partition after the 100Mb EFI partition and click on advanced button, then format, then continue and install Win8 to the first partition. 4. Run Windows update. 5. Install security suite and other apps. Basically get it working well. Something you might also want to consider if installing on a SSD is installing your user / app data files to a separate HDD while in the process of installing Win8 - see http://www.eightforums.com/tutorials/4275-user-profiles-relocate-another-partition-disk.html Or, as an alternative to this rather involved procedure, add another drive/partition to the Libraries and make this drive/partition/folders the default save destination for all of your apps. Once you have Win8 to your liking, boot with UniBeast and install OS X Mountain Lion to the second partition. Update to latest version and run MultiBeast, either EasyBeast or UserDSDT/DSDT Free, selecting the other kext files you need for your board. Something you might also want to consider if installing on a SSD is installing your user / app data files to a separate HDD - see http://lnx2mac.blogspot.com/2010/09/moving-os-x-users-to-separate-partition.html If you want, reverse the procedure above and change the HDD/SSD format to OS X first and Win8 second. Then install either one first and the other second. One thing to keep in mind is if you install Mountain Lion first, then install Win8, the Win8 installer overwrites the boot files. You will need to boot with UniBeast or rBoot and re-install Chimera. You might also, depending on your HDD (those with Boot0 error problems), need to clone your OS X install to another drive, boot the clone and install Chimera to the original from the clone.