Here's some info on installing Windows 8 Pro on a Samsung Series 5 Ultrabook, in case anybody else has one and they wanna reinstall Windows from scratch.
To get the basics out of the way first:
My particular laptop (the 13.3" variety) includes a 500GB hard drive and a 32GB SSD drive, which apparently is the ExpressCache drive. This is important.
So first, how to get Windows 8 to actually attempt to install. You can't just boot a vanilla DVD or USB, because the installer will see the OEM product key baked into the BIOS, and complain because it's for Core Edition and you're trying to install Pro Edition.
You need to make a USB installer for Windows 8 using the "Windows 7 DVD/USB Tool" (Google it). This is because you have to add a text file to the USB. You might be able to modify an ISO to add the text file to it, but you're on your own there.
Open Notepad, and create a text file named "PID.txt", and put this in as its contents:
[PID] Value=XXXXX-XXXXX-XXXXX-XXXXX-XXXXXSubstitute the X's for your Windows 8 Pro product key. Place the text file in the Win8 USB under the "sources" directory, for example
Now when you boot from the USB, Windows will use that product key instead of looking in the BIOS. And the installation will continue as normal.
But, it won't boot from disk after the installation is done. This is because the Windows Installer saw the 32GB ExpressCache disk, and it installed its bootloader onto that disk instead of onto the primary hard drive. The problem with this is that the BIOS on the laptop can't see the ExpressCache disk, and so it can't boot Windows from it.
I saw a couple solutions floating around the Internet for this. One solution said to format the ExpressCache disk with a Mac OS X file system, so that Windows wouldn't make use of it for its bootloader. You could probably format it with a Linux filesystem as well and get the same result. In this case, Windows 8 would've installed the bootloader directly onto the primary hard drive, and the BIOS would be able to boot it. This isn't much help to you, though, if you don't already have Windows installed to be able to format this partition.
What I did instead when I got to this point was... go ahead and install Linux. When I installed Windows 8, I gave it a 128GB partition on the hard drive. I gave Linux the remaining space to partition up as it pleases. When Linux installs the GRUB bootloader, it installs it onto the primary hard drive. This means the BIOS is able to boot GRUB... and, GRUB is able to see the Windows 8 Bootloader on the ExpressCache disk. Score! So now you can boot either Linux or Windows from GRUB.
This is what worked for me, anyway. If you don't wish to dual-boot Linux on your laptop, you may want to just boot a Linux LiveCD/USB, format the ExpressCache disk (/dev/sdb, probably) with a Linux filesystem like ext4, and then run the Windows installer again. Theoretically, Windows won't touch the ExpressCache disk to install its bootloader, and will install it on the primary disk. No guarantees that will work, though, as I haven't tested it.