I have Xubuntu 14.04 installed on my computer and I have 3 partitions in it. /boot, /sda1 (main, 900gb), and /swap (for swap space). I've been trying to install Windows 7 Ultimate 64-bit by following the insturctions here: https://askubuntu.com/questions/6317/how-can-i-install-windows-after-ive-installed-ubuntu (Peachy's answer)
What I did was I shrunk /sda1 to 700gb and created a new partition, NTFS formatted, that can hold 200gb for my Windows installation using GParted live (USB boot). It went smoothly.
After all this, I logged in to my (no GRUB, weird) Xubuntu just to check if it still works. It does
Now, I had an .iso file of Windows 7 and I burnt it into my DVD+RW CD at the slowest speed possible. It was successful as well.
Now here comes the weird part. I restarted my computer and opened up the BIOS to make CD booting the first priority... however, there was no options for CD booting! Weird! So I googled the problem and I saw an article that said that I should have CSM enabled. So I did. After the next restart, I was able to boot using the CD and the Windows 7 installer setup popped up on my screen.
Finally! Right? No. I tried installing Windows 7 on the unallocated space and it said: Windows cannot be installed to this disk, the selected disk is of the GPT partition style. Some articles said to disable CSM so that I can install Windows but if I do then, then I won't be able to boot my CD!
I'm not really sure where to go from here. Some articles talk more about BIOS and UEFI which I really don't understand that much.
It was easy for me before to install a Linux OS when Windows is already installed but the other way around seems too difficult.
My laptop is an ASUS X550LB if that helps.