SetCursorPos works in general on Windows 8.1, but you may have found an edge case which doesn't work as expected. Can you provide more information about the scenario you are having problems with? We'd need at least a code snippet to go along with the
scenario description, but if you can provide a minimal test project on your SkyDrive that would be even better.
I just ran a quick test app on Windows 8.1 (RTM) which set a timer to call SetCursorPos(100,100) ever second and it worked as expected: the cursor warped to 100,100 every time the timer triggers.