Trying to install Window 8 on a separate partition alongside Ubuntu, I got the message "Windows cannot be installed to this disk. Your computer hardware may not support booting to this disk. Ensure that the disk controller is enabled in the computer's BIOS menu." My system doesn't use EFI or GPT, which cause known issues with Windows installation.
Windows must be installed to a primary partition, not an extended or logical partition.
I checked the error log (in X:\Windows\panther\ I believe), and it says that the partition is large enough but it is not a primary partition. Yet in Windows installation, even when I delete the partition and recreate it, it's created as a logical not a primary partition. Also,in GParted, I can't change the partition type from logical to primary, though I flagged it as "boot".
Finally I discovered that no, primary partitions can't be created inside an extended partition. So using GParted, I shrank my extended partition and moved it to the right/end of the drive, and created a NTFS partition to the left/at the beginning of the drive. I could install Windows 8 on that partition.