You can download Win 8 for $40. If you have an older machine with Vista it’s probably worth doing the upgrade, as long as you have the memory and hardware that can handle it.
As I understand it, W8 requires fewer resouces than WVista, being targeted more at "mobile" devices. I've got an ASUS EEE PC "convertible" netbook that also can function as a tablet (screen rotates and swivels to lie flat over the keyboard) that has a touchscreen and W7. I'm thinking about putting W8 on it just to get an idea of W8's performance.
MSoft's "will it run here" program says that W8 will run on it, but that the touchscreen "isn't fully compatible".