I have a 60GB SSD + 1TB HDD on my laptop. I want to know if I could keep Windows 8 on my SSD and install Ubuntu on HDD. Can GRUB detect both operating systems?
Yes. As long as both disks are mounted at the time grub is installed/configured it will detect them (and if not, there are enough topics on this site to help you out with that).
Oh yes and it's better to install Ubuntu after you have installed Windows so that grub can handle both of them. But on the contrary you may want to install grub again to detect your Windows as well.