What version of Windows 8 are you trying to install?
I tried to install windows 8.1 and even windows 10 technical preview from Microsoft both same error
I don't think it's a requirement for VT-x if you're installing Windows 8 directly on the hard drive.
AFAIK VT-x is only needed when you're virtualizing, such as running software like VMware and VirtualBox
Oh yeah, that's true, that error is in Virtualbox but when i try to install it directly on a hard drive it shows me this
Error on the all versions from windows 8 straight up
I have Core 2 Duo E7400 (2.8 Ghz), and Asus P5KPL AM/PS. A very old computer which I doubt meets the specification of Windows 8.1 but it works just fine.
How do you managed to install it?