How to dual boot Win8/Ubuntu using UEFI and two HDDs

I think what you want to do would be a little bit simpler than doing an install on one drive. I assume you are familiar with some more advanced terminology here since you said you were reading up on the subject, but please ask if anything is unclear.

You need to first get your install ISO's downloaded: --Getting a Windows 8 install ISO may be the hardest part of this procedure. (But you don't need if it is already installed.) --Ubuntu desktop ISO. (I presume you want Ubuntu 14.04 / amd64 because your computer is 64 bit). If possible, create two bootable usb sticks, one for each. You can easily have a second computer handy to switch from one bootable iso to another and use just one usb drive, or once you install windows, download Lili usb creator and create the Ubuntu install drive. Alternatively you could make DVD's if your target computer has a DVD drive.

You need to disable secure boot in your bios. If Windows 8 is already installed, it is easy to find a guide for this. (For the love of your sanity, don't format the Windows 8 already installed.) You have to shift-right-click restart in the lower right corner power menu to get to Advanced settings and access the bios. Please note the menu progression is totally different twixt 8 and 8.1. While in the bios turning off Secure boot, your bios might have an option to allow you to turn on F8/F10/F12/or del key to let you access the bios, which Windows 8 PC's have to ship with the option off. (This is for convenience as you probably need to go into the bio a lot as a dual booter.)

IF you are totally installing both OS's, you have the option to turn the UEFI off in the bios. But this is not advisable because UEFI protects you from rootkit "viruses".

We also need to do some planning. We ultimately need the bios to boot first to the SSD drive. However, we will install each OS separately with only one drive attached at a time, so this can be a last step for you.

We want the Linux drive to be the primary boot drive because if we can avoid replacing a part of the windows boot system with GRUB2, we should. Windows gets cranky when it doesn't find what it expects in the boot sectors of the drive when it goes sniffing around to auto-fix itself. So we can prevent that conflict from ever happening.

If you are planning partitions, there is something important to think about. If you have Windows 8 fast boot turned on, Ubuntu cannot read the Windows partition. This means that if you want to share files, you need to plan on having an NTFS or FAT32 partition that they both can share nicely. Also, hibernating windows and booting Linux will cause Windows to lock Ubuntu out of any hard drive that a Windows program had just one file open on--> perhaps on the nice little data sharing hard drive partition you set up. So don't hibernate and then boot Ubuntu. (Yes, I learned this the hard way...)

You want to install Windows 8 first. The key trick is to only have the one hard drive you plan to use for Windows connected. I think that you already have Windows 8 installed on the HD and are adding the SSD? If this is the case, you are done installing Windows, hurray! However, you will need to disable Secure Boot. (as above)

Now, power down the computer and disconnect the Windows 8 hard drive and attach the Linux hard drive. Install Linux.

After it is installed and you get online, run these commands in terminal

sudo add-apt-repository ppa:yannubuntu/boot-repair
sudo sed 's/trusty/saucy/g' -i /etc/apt/sources.list.d/yannubuntu-boot-repair-trusty.list
sudo apt-get update
sudo apt-get install -y boot-repair

Boot-repair is going to get the whole thing dual booting later.

Now, power down and attach both hard drives. Set up bios so that we boot to the SSD/Linux. (If your bios setting is wrong, you'll just go to windows instead. No problem try again.)

Now that we are happily booting Linux, run boot-repair and follow the instructions. This should set up your boot menu to let you switch between the OS's. And ta-da, all done.

Now if for some reason boot-repair goes all haywire on you, first of all, you can just tell the bios to switch to Windows and there you go, you can still boot something. Also, you can use your Ubuntu 14 desktop usb stick to boot to Ubuntu. Select try Ubuntu. Then you can install boot-repair per the above instructions and try again.